Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-02-17
2003-03-04
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C252S062200, C204S421000
Reexamination Certificate
active
06528195
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mixed ionic conductor and an electrochemical device, such as a fuel cell or a gas sensor, using the same.
2. Description of the Prior Art
The applicant has long been actively developing mixed conductors of protons and oxide ions (see for example Publication of Unexamined Japanese Patent Application (Tokkai) No. H5-28820 or H6-231611). These mixed ionic conductors are basically perovskite oxides containing barium and cerium wherein a portion of the cerium has been substituted by the substitute element M, so as to achieve a high ionic conductivity (chemical formula: BaCe
1−p
M
p
O
3−&agr;
). Especially, when the substitution amount p of the substitution element M is 0.16 to 0.23, the mixed ionic conductor has a high conductivity, higher even than zirconia-based oxides (YSZ: yttrium-stabilized zirconia), which conventionally have been used as oxide ionic conductors. As the substitution element M, rare earth elements are suitable, in particular heavy rare earth elements, because of their atomic radius and charge balance.
New fuel cells, sensors and other electrochemical devices using such materials as a solid electrolyte have been developed. The sensor characteristics and the discharge characteristics of fuel cells using such materials have been shown to be superior to prior devices. Other patent applications related to these materials are Tokkai H5-234604, Tokkai H5-290860, Tokkai H6-223857, Tokkai H6-290802, Tokkai H7-65839, Tokkai H7-136455, Tokkai H8-29390, Tokkai H8-162121, and Tokkai H8-220060.
However, these materials show some problems with regard to their chemical stability. For example, barium tends to precipitate in CO
2
gas. To solve these problems, the applicant has proposed a counter-strategy in Tokkai H9-295866. However, even this counter-strategy is not perfect, and for example at low temperatures of 85° C. and 85% humidity, precipitation can be observed in shelf tests and boiling tests in water. Moreover, under high water vapor pressures as during discharge of the fuel cells, barium can be seen to precipitate near the platinum electrodes. Furthermore, with gas sensors, there is the problem of maintaining high ion conductivity at lower temperatures over a long time and the problem of raising the acid resistance of the oxide itself.
SUMMARY OF THE INVENTION
To solve these problems, it is an object of the present invention to improve the chemical stability of the mixed ionic conductors.
The main cause for decomposition of the oxides due to humidity is believed to be the fact that the segregated barium turning into barium hydroxide reacts with the carbon dioxide, and forms stable barium carbonate. To increase the moisture resistance, the present invention uses a mixed ionic conductor including the following perovskite structure oxide.
A mixed ionic conductor of one embodiment of the present invention (a first ionic conductor) includes an ion conductive oxide having a perovskite structure of the formula Ba
a
(Ce
1−b
M
1
b
)L
c
O
3−&agr;
, wherein
M
1
is at least one trivalent rare earth element other than Ce;
L is at least one element selected from the group consisting of Zr, Ti, V, Nb, Cr, Mo, W, Fe, Co, Ni, Cu, Ag, Au, Pd, Pt, Bi, Sb, Sn, Pb and Ga;
with
0.9≦a≦1;
0.16≦b≦0.26;
0.01≦c≦0.1;
and
(2+b−2a)/2≦&agr;<1.5.
In this mixed ionic conductor it is preferable that M
1
is at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y and Sc. More preferably, M
1
is Gd and/or Y.
It is also preferable that L is at least one element selected from the group consisting of Zr, Ti, Fe, Co, Ni, Cu, Bi, Sn, Pb and Ga. More preferably, L is at least one element selected from the group consisting of Zr, Ti, Bi, Pb and Ga.
A mixed ionic conductor of another embodiment of the present invention (a second ionic conductor) includes an ion conductive oxide having a perovskite structure of the formula Ba
e
Zr
1−z
M
2
z
O
3−&bgr;
, wherein
0.9≦e≦1;
M
2
is at least one element selected from the group consisting of trivalent rare earth elements, Bi, Ga, Sn, Sb and In;
with
0.01≦z≦0.3;
and
(2+z−2e)/2≦&bgr;<1.5.
In this mixed ionic conductor it is preferable that 0.16≦z≦0.3. It is also preferable that M
2
is at least one element selected from the group consisting of trivalent rare earth elements and In, especially elements selected from the group consisting of Pr, Eu, Gd, Yb, Sc and In.
A mixed ionic conductor of yet another embodiment of the present invention (a third ionic conductor) includes an ion conductive oxide having a perovskite structure of the formula Ba
d
Zr
1−x−y
Ce
x
M
3
y
O
3−&ggr;
wherein
M
3
is at least one element selected from the group consisting of trivalent rare earth elements, Bi and In;
with
0.98≦d≦1;
0.01≦x≦0.5;
0.01≦y≦0.3;
and
(2+y−2d)/2≦&ggr;<1.5.
In this third mixed ionic conductor, it is preferable that M
3
is at least one element selected from the group consisting of Nd, Sm, Eu, Gd, Tb, Yb, Y, Sc and In. More preferably, M
3
is at least one element selected from the group consisting of Gd, In, Y and Yb.
The mixed ionic conductors of the present invention have not only the necessary conductivity for electrochemical devices such as fuel cells, but also superior moisture resistance.
Throughout this specification, “rare earth element” means Sc, Y, and the lanthanides (elements
57
La through
71
Lu). In the above formulas, &agr;, &bgr; and &ggr; are determined by the absent amount of disproportionate oxygen.
The present invention also provides devices using such a mixed ionic conductor. A fuel cell in accordance with the present invention includes as a solid-state electrolyte a mixed ionic conductor as described above. A gas sensor in accordance with the present invention includes as a solid-state electrolyte a mixed ionic conductor as described above. Using the mixed ionic conductors of the present invention provides electric devices, such as fuel cells and gas sensors, with high moisture resistance, high performance, and long lifetimes.
REFERENCES:
patent: 5387330 (1995-02-01), Taniguchi et al.
patent: 0 677 741 (1995-10-01), None
patent: 5-28820 (1993-02-01), None
patent: 5-234604 (1993-09-01), None
patent: 5-290860 (1993-11-01), None
patent: 6-223857 (1994-08-01), None
patent: 6-231611 (1994-08-01), None
patent: 6-290802 (1994-10-01), None
patent: 7-65839 (1995-03-01), None
patent: 7-136455 (1995-05-01), None
patent: 8-29390 (1996-02-01), None
patent: 8-162121 (1996-06-01), None
patent: 8-198670 (1996-08-01), None
patent: 8-220060 (1996-08-01), None
patent: 8-327592 (1996-12-01), None
patent: 9-27330 (1997-01-01), None
patent: 9-295866 (1997-11-01), None
Ryu et al. (“Chemical stability and proton conductivity of doped BaCe3-BaZrO3 solid solutions,” Solid State Ionics 125 (Oct. 1999), pp. 355-367).*
HCA abstract of the Ryu et al. reference (“Chemical stability and proton conductivity of doped BaCe3-BaZrO3 solid solutions,” Solid State Ionics 125 (Oct. 1999), pp. 355-367).*
Weinstroer et al., “Investigation of the influence of zirconium substitution on the properties of neodymium-doped barium cerates”, Solid State Ionics, vol. 101-103 (1997) pp. 1113-1117, No Month Available.*
European Search Report—Application No. EP 00301251 dated Jul. 21, 2000.
Chaney Carol
Tsang-Foster Susy
LandOfFree
Mixed ionic conductor and device using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mixed ionic conductor and device using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mixed ionic conductor and device using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3060684