Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1995-10-26
1997-01-07
Nuzzolillo, M.
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 40, 429 45, 429 46, 429 30, H01M 812
Patent
active
055915370
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a solid oxide fuel cell comprising a cathode, a YSZ electrolyte and an anode, where the cathode is composed of a mixture of LMS and YSZ.
BACKGROUND ART
It is known from Solid State Ionics 57 (1992) 295-307 North-Holland to produce LaMnO.sub.3 electrodes containing YSZ electrolyte. LaMnO.sub.3 powder is mixed with YSZ in the ratio 1:1. The addition of YSZ reduces the polarisation resistance and improves the efficiency. The polarisation resistance was reduced to 0,18.OMEGA..cndot.cm.sup.2 at 64 mV and approximately 900.degree. C.
Furthermore European Patent Document; and EP 424,814 discloses a solid oxide fuel cell where the cathode is composed of a mixture of LSM and YSZ, the YSZ being stabilized by means of 8 to 10 mol % of Y.sub.2 O.sub.3. As a result the polarisation resistance is slightly reduced.
DESCRIPTION OF THE INVENTION
The object of the invention is to provide a solid oxide fuel cell with a lower polarisation resistance than previously known. The solid oxide fuel cell must furthermore be easy to produce.
A solid oxide fuel cell of the above type is according to the invention characterised by the content in the cathode of YSZ amounting to 20-75% by weight, and by the YSZ of the cathode containing less Y.sub.2 O.sub.3 than the YSZ of the electrolyte, preferably less than 8 mol % of Y.sub.2 O.sub.3, especially approximately 3 mol % of Y.sub.2 O.sub.3. As a result the polarisation resistance can be reduced to 0,08.OMEGA..cndot.cm.sup.2 or less at 40 mV at approximately 1000.degree. C. Furthermore a mechanically stable structure is obtained.
Furthermore Mn may according to the invention be added to the cathode material in excess. In this manner a further reduction of the polarisation resistance is rendered possible under predetermined circumstances. Moreover a layer of LSM may according to the invention be sintered on the outside of the cathode.
BRIEF DESCRIPTION OF THE INVENTION
The invention is explained in greater detail below with reference to the accompanying drawings, in which
FIG. 1 illustrates a solid oxide fuel cell according to the invention,
FIG. 2 illustrates an equivalent circuit,
FIG. 3 illustrates a dilatometric curve of a YSZ sheet,
FIG. 4 shows a measurement of the electrode impedance illustrating that the polarisation resistance (i.e. the portion of the horizontal axis found below the curve) is 0.08.OMEGA..cndot.cm.sup.2 at the illustrated conditions,
FIG. 5 illustrates a set-up for testing a solid oxide fuel cell,
FIG. 6 illustrates an electric circuit for testing the cell,
FIG. 7 illustrates a conductor path pattern forming a current collection network on the electrode,
FIG. 8 illustrates the voltage measured at the center of the cell and at the rim of the cell, respectively, versus the current intensity,
FIG. 9 illustrates an electric equivalent circuit resulting from division of the cell into five concentric rings,
FIG. 10 illustrates the distribution of current and voltage drop between five annular portions of the cell, and
FIG. 11 illustrates current density functions from the center to the rim.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
Parameters, such as temperature, oxygen partial pressure, heat treatment, porosity, electrode thickness, composition and particle size of the cathode material are of vital importance for the efficiency of a fuel cell because the packing density of the cathode material depends on these parameters.
The reaction resistance during an oxygen-reducing process depends on the number of triple contact points, where gas, electrolyte, and electrode can be brought into contact with each other with the result that an electro-chemical reaction can take place. Thus, the reaction resistance depends on the packing density of the layer of cathode material being in direct contact with the electrolyte.
Electro-chemical impedance measurements have been used for studying the efficiency of La.sub.1-x Sr.sub.x MnO.sub.3 (LSM)--based cathodes at 1000.degree. C., pO.sub.2 =0.21 atm and a polarisation o
REFERENCES:
patent: 5057362 (1991-10-01), Schroder et al.
patent: 5306411 (1994-04-01), Mozanec et al.
patent: 5453330 (1995-09-01), Kawasaki et al.
patent: 5500307 (1996-03-01), Anzai et al.
Kenjo et al, "LaMnO.sub.3 air cathodes containing ZrO.sub.2 electrolyte for high temperature solid oxide fuel cells", Solid State Ionics 57 (1992), North-Holland, pp. 295-302 (month N/A).
Bagger Carsten
Kindl Bruno
Mogensen Mogens
Forskningscenter RIS.O slashed.
Nuzzolillo M.
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