Chemistry: electrical current producing apparatus – product – and – Having earth feature
Reexamination Certificate
1998-08-19
2001-05-15
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having earth feature
C429S047000, C429S047000, C429S047000
Reexamination Certificate
active
06232009
ABSTRACT:
The invention relates to an electrochemically active element for high temperature fuel cell in accordance with the preamble of claim
1
and to a fuel cell battery.
High temperature fuel cells are known—see for example EP-A 0 714 147 (=P.6651)—in which the electrochemically active element, the so-called PEN, is formed as a self supporting plate, which is however very thin and extremely fragile. The PEN consists of a positive electrode (P), an electrolyte (E) and a negative electrode (N). The positive electrode or cathode is arranged at the air side, the negative electrode or anode at the gas side. The PEN is a separate element which can be built into the fuel cell battery. Because of its fragility the assembly of the battery is difficult.
The electrolyte, which conducts oxygen ions at the operating temperature of about 900° C., consists of stabilised zirconium oxide (ZrO
2
) to which further substances have been added to improve the mobility of the oxygen ions, namely for example 3 to 12
mol
/
o
(mole percent) Y
2
O
3
. One can also add A
2
O
3
(2 to 20
mol
/
o
) in order to obtain a greater strength of the electrolyte layer.
The electrodes are applied to the electrolyte layer by sintering on, first the anode at a sintering temperature of about 1250-1450° C., then the cathode at a lower sintering temperature (1100-1300° C.). Through the influence of the high temperature during the sintering of the anode material a grain growth takes place in the electrolyte layer, through which this layer becomes more brittle and more fragile. Special care must therefore be taken when the battery is assembled. Cracks can also form in the PEN during operation, in particular if the temperature is lowered and then raised again in repeated interruptions of the operation.
The object of the invention is to provide an electrochemically active element for a high temperature fuel cell which is less fragile than the known PENs. this object is satisfied by the element characterised in claim
1
.
The electrochemically active element (
1
) for a high temperature fuel cell is designed in layers and comprises an anode layer, a cathode layer and an electrolyte layer which is arranged therebetween. The electrolyte is a ceramic material of zirconium oxide ZrO
2
stabilised with yttrium Y which can also contain aluminium oxide Al
2
O
3
in addition. The anode is manufactured from a power mixture through sintering on the electrolyte layer. This anode mixture contains the oxides NiO and CeO
2
and can contain an oxide of the type A
2
O
3
, with for example A=Sm, Y, Gd and/or Pr. In accordance with the invention 0.5-5
mol
/
o
CoO, FeO and/or MnO is or are to be added to the anode mixture in order to lower the sintering temperature of the mixture.
Thanks to the lowering of the sintering temperature in the manufacture of the anode as a result of the measure in accordance with the invention, the crystal growth in the electrolyte is less strongly pronounced so that the original strength of the electrolyte layer is largely retained.
The dependent claims
2
to
10
relate to advantageous embodiments of the element in accordance with the invention. The subject of claim
11
is a fuel cell battery with elements in accordance with the invention.
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Alejandro R
Kalafut Stephen
Sulzer Hexis AG
Townsend & Townsend & Crew LLP
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