Solid electrolyte structure

A solid electrolyte structure for fuel cells and other electrochemical devices providing oxygen ion transfer by a multiplicity of exposed internal surfaces made of a composition containing an oxide of a multivalent transition metal and forming small pore-like passages sized to permit oxygen ion transfer while limiting the transfer of oxygen gas.

BACKGROUND OF THE INVENTION 
This invention relates to oxygen ion conducting electrolytes having 
enhanced oxygen ion transfer, and to electrochemical devices having an 
oxygen-rich electrode and an oxygen-deficient electrode in association 
with the inventive electrolyte, and more particularly to electrochemical 
devices including fuel cells having a multiplicity of internally exposed, 
oxygen ion transfer surfaces within an electrolyte zone to improve the 
oxygen ion transfer rate between the electrodes. More specifically, the 
invention relates to solid electrolyte fuel cells operable at reduced 
temperatures in the order of about 200.degree.-800.degree. C. and having a 
multiplicity of internal passages or pores to enhance oxygen ion transfer. 
The pores are sized to limit gas transfer but permit oxygen ion transfer 
along the surfaces of pores in a lateral direction from the oxygen 
electrode or cathode towards the fuel electrode or anode. 
Typical solid electrolyte fuel cells utilize a porous fuel anode, a porous 
oxygen cathode and a crystalline electrolyte. Their operating temperatures 
are usually about 1000.degree. C. in order that an adequate quantity of 
oxygen ions are transferred per unit time across an oxygen ion transfer 
gradient in the electrolyte by "hopping" between oxygen vacancies within 
the crystal structure. Usually, the electrodes have good electronic 
conductivity while the electrolyte has poor electronic but good ionic 
conductivity. In general, these solid electrolyte fuel cells have been 
identified with problems in performance and natural stability associated 
with the high operating temperatures. 
A number of developments have been carried out to reduce the high operating 
temperatures and other problems associated with these solid electrolyte 
fuel cells. In U.S. Pat. No. 4,024,036 a heteropoly acid represented by 
the formula 
EQU H.sub.m [X.sub.x Y.sub.y O.sub.z ]nH.sub.2 O) 
has been disclosed as a proton permselective electrolyte. In the above 
formula, X includes a variety of metals including transition metals while 
Y is a transition metal but not the same as X. 
In U.S. Pat. No. 3,300,344, a fuel cell is disclosed with a solid 
gas-impervious electrolyte compound of ZrO.sub.2 and Y.sub.2 O.sub.3 which 
has oxide vacancies for transfer of the oxide ion through the solid 
electrolyte, and with porous electrodes. For the cathode, a porous 
nonconductive matrix of the electrolyte composition is loaded with 
manganese oxide to improve electrical conductivity. 
Other disclosures of interest may be found in U.S. Pat. No. 3,684,578; U.S. 
Pat No. 4,277,360, U.S. Pat No. 4,197,171 and U.S. Pat. No. 3,410,728. 
At lower temperatures in the order of 600.degree.-800.degree. C., molten 
carbonate fuel cells with molten carbonates melting in the range of about 
400.degree.-700.degree. C. are preferred over solid electrolyte fuel cells 
to achieve acceptable output current levels. The transfer of oxidant ions 
in the molten carbonate fuel cells is achieved by the initial formation of 
oxygen ions followed by their combination with carbon dioxide to form 
carbonate ions as a means of transferring the oxygen ions across the 
electrolyte. An initial conditioning of the cell is normally carried out 
at about 650.degree. C. for about one to two hundred hours (and usually 
about 50 hrs) to achieve normal performance levels associated with a 
plateau on the performance curve. After the conditioning period, the 
operation of the cell tends to be limited by the rate at which carbonate 
ions form. In general, the molten carbonate fuel cells have problems 
associated with the initial conditioning period, the maintenance of the 
molten carbonate, and corrosion of cell components by the molten 
carbonate. 
One object of this invention is an oxygen transport electrolyte with 
enhanced oxygen ion transfer properties. A second object of this invention 
is an electrochemical device with a solid electrolyte structure providing 
oxygen ion transfer and operable at temperatures below about 1000.degree. 
C. A third object of the invention is a molten carbonate fuel cell 
operable at temperatures below about 800.degree. C. Another object of the 
invention is a molten carbonate fuel cell with an improved oxygen ion 
transfer rate. Yet another object of the invention is a fuel cell with a 
solid electrolyte. Still another object of the invention is a molten 
carbonate fuel cell operable at temperatures below about 800.degree. C. 
with reduced conditioning requirements to achieve plateau operating 
performance. An additional object of the invention is a solid electrolyte 
fuel cell operating in the absence of molten carbonate yet operable at 
temperatures below 1000.degree. C. and preferably below about 800.degree. 
C. A further object of the invention is a solid electrolyte fuel cell with 
desirable characteristics of oxygen ion transfer within a solid 
electrolyte structure. A further object of the invention is an 
electrochemical cell operating with a solid electrolyte and an oxygen-rich 
electrode and a second, oxygen-deficient electrode for gas sensing and 
electrolytic oxygen-pumping applications. 
SUMMARY OF THE INVENTION 
Briefly, the invention is directed to a solid electrolyte structure for 
electrochemical cells and to an electrochemical device having an oxygen 
electrode, a fuel electrode, and ion transfer means for accepting oxygen 
ions from the oxygen electrode, the ion transfer means including a solid 
electrolyte structure having a multiplicity of exposed internal surfaces 
for oxygen ion transfer. It has been found that this structure in a molten 
carbonate fuel cell with an adjacent source of transition metal for the 
electrolyte provides an improved oxygen ion tranfer and reduces the 
initial conditioning period substantially. This may in part be due to the 
recognition by the inventor that the extensive initial conditioning period 
may have caused a migration of corrosion products with metal ions from the 
cathode and cell housing to the electrolyte in previous molten carbonate 
fuel cells. With the improved oxygen ion transfer performance provided by 
the solid electrolyte of this invention, the use of the electroltye as the 
primary electrolyte in a solid electrolyte fuel cell will permit the 
operation of the cell at temperatures below about 1000.degree. C. and at 
temperatures of about 800.degree. C. and below. 
Advantageously, the solid electrolyte structure internally has a 
multiplicity of small, open pores to provide the internal surfaces with 
the pores being sized to accommodate the passage of oxygen ions but being 
generally impermeable to the passage of molecular gases and particularly 
hydrogen and oxygen. Advantageously, the structure further provides a 
composition around the pores composed of an oxide of a multivalent metal 
capable of adsorbing and desorbing and readsorbing oxygen ions to thereby 
serve as an oxygen ion transfer agent while having insulating properties 
with respect to electron transfer. In one embodiment of a solid 
electrolyte fuel cell, the electrolyte is predominantly composed of 
manganese oxides in the form of MnO.sub.2 and/or Mn.sub.3 O.sub.4 with the 
multiplicity of small, open pores being inherently formed in the 
structure. In the operation of the cell, the formation of near Mn.sub.3 
O.sub.4 near the anode provides at least a portion of the insulating 
properties with respect to electronic transfer in this embodiment. 
In the operation of an electrochemical device of the invention, oxygen ion 
conduction is provided along internal pore surfaces of the solid 
electrolyte. The oxygen ion conduction may be characterized as a 
surface-film of adsorbed oxygen ions maintained by an oxygen ion 
concentration gradient provided by an excess of oxygen ions at one 
extremity of the electrolyte, a deficiency at the other, and with a 
nominal absence of both fuel or oxidant gases over the interior portions 
of the electrolyte surfaces. While particularly useful for fuel cells, the 
application of the solid electrolyte structure of this invention 
particularly as characterized by a multiplicity of small, open pores is 
not restricted to fuel cell structures, but may be incorporated into 
oxygen sensor systems with electrode means designed for automatic 
carburetion and emission control in internal combustion engines, 
industrial combustion control, and electrolytic oxygen pumps which 
regulate or regenerate oxygen partial pressures in controlled atmospheres, 
and to other applications known to those skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION 
The electrolyte of the invention may be utilized as a component for use 
with a pair of electrodes in an oxygen sensor or electrolytic cell, or in 
combination with a pair of electrodes as in a fuel cell. Advantageously, 
the electrolyte comprises an elongated layer composed of a multiplicity of 
small, open pores sized to permit oxygen ion transfer but limit oxygen and 
hydrogen gas. Preferably, the layer has a density of about 2-5 gm/cc and 
is essentially gas-tight and is structurally and chemically stable at the 
elevated temperature. Advantageously, the inventive cell comprises one 
oxygen-rich electrode for generating oxygen ions, ion transfer means 
including a solid electrolyte structure for accepting oxygen ions formed 
on the electrode, and a second oxygen-deficient (or fuel) electrode as a 
means for withdrawing the oxygen ions from the electrolyte. Means are 
provided for introducing an oxygen-containing gas to the oxygen electrode 
and for introducing an oxygen-deficient or reducing gas to the second 
electrode. 
The ion transfer means includes a solid electrolyte structure with enhanced 
oyxgen ion transfer performance and restricted oxygen gas transfer. In an 
embodiment in a molten carbonate fuel cell, an electrolyte structure of 
ceramic composition is provided in combination with an adjacent source of 
nickel as the transition metal. During an initial heating of the cell, the 
transition metal-ion migrates to the solid electrolyte structure and 
provides enhanced surfaces exposed internally in the structure. With the 
molten carbonate providing a barrier to oxygen gas transfer, the 
electrolyte structure is primarily characterized by internal passages 
having an enhanced surface composition composed of a transition metal 
oxide. 
The term "solid electrolyte structure" is intended to refer to a solid 
structure with the extensive internal exposed surfaces providing enhanced 
oxygen ion transfer and particularly a pore structure as described herein. 
It may provide an oxygen ion transfer system in conjunction with an 
adjacent electrolyte as in a molten carbonate fuel cell or as the primary 
electrolyte as in a solid electrolyte fuel cell, or be used in an oxygen 
sensing or pumping device. In the inventive electrochemical device, the 
solid electrolyte structure preferably is predominantly composed of a 
multiplicity of small, open pores sized to permit the passage of oxygen 
ions but substantially impermeable to the passage of oxygen gas. 
Advantageously, the composition around the pores is composed of an oxide 
of at least one multivalent metal capable of adsorbing and desorbing 
oxygen ions to serve as an oxygen ion surface-transfer agent. 
The solid electrolyte structure preferably adjoins the oxygen electrode and 
serves to provide active internal surfaces for the transfer of oxygen ions 
laterally away from the electrode. The solid electrolyte structure may be 
used with a separate electrolyte as in a molten carbonate fuel cell or may 
serve as the primary electrolyte and extend between the electrodes as in a 
solid electrolyte fuel cell. 
In general, the pores are sized below about 1.times.10.sup.4 .ANG. and 
preferably about 5-100 .ANG.. These pores extend in a lateral direction 
from the oxygen electrode. In a fuel cell, the pores may extend 
substantially across the electrolyte although the oxygen ions are consumed 
as they react with the hydrogen ions (or hydrogen gas) at or near the 
anode. The pores may extend as continuous pores or may be formed of a 
series of individual pores forming a twisting path across the structure. 
As in several forms of manganese oxide, the pores may be an inherent part 
of the structure. In some instances, the structure may be formed of 
particles of a material compacted together to form the pore structure. 
Also, the pores may be formed by compacting dense inorganic powders with 
contiguous decomposable fiber networks which are removed by heating the 
material to an elevated temperature. 
Suitably, the solid electrolyte structure may be composed of a metallic 
oxide containing one or more multivalent metal ions and having the desired 
porosity. Ceramic oxides provide many advantages, particularly those 
containing one or more of the transition metal ions and particularly those 
capable of variable valences of 3 and above. The structure may contain 
other components such as alkaline metal ions in addition to the 
multivalent metallic oxide as the oxygen ion transfer agent or it may be 
composed predominantly of the desired metallic oxide. 
Suitable oxides of multivalent metals include the transition metals of 
Periods 4, 5 and 6 of the Periodic Table such as manganese, cobalt, 
nickel, copper, iron, zinc, vanadium, chromium, titanium, molybdenum, 
ruthenium, rhodium, palladium, iridium, rhenium, osmium and platinum, and 
the like and nontransition metals including the stably-trivalent Group 3A 
and 4A metals which are capable of forming a substrate for the 
incorporation of variably-valent oxides and primarily aluminum and tin. 
Preferably, the transition metal is manganese, nickel, titanium, vanadium, 
chromium, or molybdenum. Other univalent metal cations such as Li, K, Rb 
and Cs may also be present. In general, the oxide may be expressed as 
EQU T.sub.a X.sub.b O.sub.c 
wherein T is a transition metal, X is the transition metal, Al, Sn, and an 
alkali metal such as Li, K, Rb, Cs, and the integers a, b, and c represent 
the number of atoms to balance the formula. Illustrations of these oxides 
include the transition metal oxides where X equals T as in MnO.sub.2, NiO, 
CoO, CuO, Fe.sub.2 O.sub.3, ZnO, V.sub.2 O.sub.5, TiO.sub.2, MoO.sub.3, 
RuO.sub.2, PdO, IrO.sub.2, Re.sub.2 O.sub.7, OsO.sub.2, PtO.sub.2 and the 
like. Where X is not a transition metal, illustrations include MnAl.sub.2 
O.sub.5, NiAl.sub.2 O.sub.4, CoAl.sub.2 O.sub.4, CuAl.sub.2 O.sub.4, 
FeAlO.sub.3, ZnAl.sub.2 O.sub.4, VAlO.sub.4, TiAl.sub.2 O.sub.5, 
MoAl.sub.2 O.sub.6, RuAl.sub.2 O.sub.5, PdAl.sub.2 O.sub.4, IrAl.sub.2 
O.sub.5, ReAlO.sub.5, OsAl.sub.2 O.sub.5, PtAl.sub.2 O.sub.5, MnSnO.sub.4, 
MoSnO.sub.5, LiMn.sub.8 O.sub.16, KMn.sub.8 O.sub.16 and the like. 
The structure forming the internal surface includes an oxygen ion transfer 
agent which operates under an oxygen ion gradient source of at or near the 
cathode and depleted towards the anode. The oxygen-ion transfer agent is 
composed of a multivalent transition metal compound in which the 
transition metal is capable of changing valences, or alternatively, is 
capable of "hole formation" at or near its resident position in the 
lattice. 
In prior art molten carbonate cells, migration of nickel or other metal 
during the conditioning process may transfer a metal to the electrolyte 
structure. However, this may limit the operation of the cell since 
hydrogen reaction with the transition metal may form undesirable deposits. 
Previously, manganese dioxide has been utilized in low temperature 
batteries in the form of a wet paste adjacent a carbon electrode and has 
served as a source of hydroxide ions which have been transferred within 
the wet mixture. In the process, MnO.sub.2 is reduced in oxygen content 
and converted to Mn.sub.3 O.sub.4. 
In the molten carbonate fuel cell of this invention the rate is 
reproducibly accelerated by the incorporation of a reactive source of 
transition metal ions (in the form of a thin layer of partially-reduced 
spinel) at the cathode-tile interface. Thus the transfer agent is 
incorporated into the tile structure without the extensive conditioning 
required in the prior art cell. For solid electrolyte fuel cells, the 
solid electrolyte provides the structure in a form with improved oxygen 
ion transfer agent to permit the operation of the cell at a temperature 
below about 1000.degree. C. Advantageously, the structure has internal 
passages or channels with surfaces of the desired composition and sized to 
permit the transfer of labile oxygen ions weakly adsorbed on the surface 
while being limited and preferably impermeable to the diffusional transfer 
of oxidant or fuel gases as molecular species in the free volume of the 
channels or particle interstices of the "solid" electrolyte. For solid 
electrolyte fuel cells, the solid electrolyte structure of the invention 
provides an increased oxygen ion transfer rate permitting operation of the 
cell at temperatures below about 1000.degree. C. and advantageously about 
200.degree.-800.degree. C. 
In the oxygen ion transfer, the multivalent transition metal ion acts to 
accommodate the residence of an oxygen ion concentration gradient on at 
least a portion of the solid electrolyte surface structure. As an 
illustration, the oxides of manganese may serve as the composition for an 
electrolyte of a solid electrolyte fuel cell. At the cathode, MnO.sub.2 
may be the predominant composition, while Mn.sub.3 O.sub.4 may be present 
within the structure a distance from the cathode. Further, both MnO.sub.2 
and Mn.sub.3 O.sub.4 are advantageous since their structures include pores 
of suitable size, Mn.sub.3 O.sub.4 is not reduced to metallic manganese by 
exposure to hydrogen at 650.degree. C., and Mn.sub.3 O.sub.4 provides 
electron insulating properties to the composition. 
The oxides of manganese were shown to have an additionally advantageous 
characteristic in providing large areas of inner-channel surface which 
offer a monoenergetic adsorption potential to adsorbed species along the 
surface of the channel. FIG. 4 is a graph based on test data which show 
reduced adsorption isotherm for water vapor on a powdered aggregate sample 
of 50 m.sup.2 /g synthetic cryptomelane (KMn.sub.8 O.sub.16 nH.sub.2 O), 
activated at 125.degree. C. with adsorption carried out at 20.degree. C. 
The FIG. 4 follows the Type III adsorption isotherm characteristic of 
weakly-bound adsorbate-to-adsorbent coupling. The lower cusp extending 
over the formation range of the first physically adsorbed layer is 
indicative of adsorbate behavior as a two-dimensional gas on the surface 
prior to monolayer formation. This requires a monoenergetic surface 
characteristic inherent in the adsorbent substrate. It thus provides the 
fuel cell of this invention with an improved oxygen-ion conduction means 
not requiring high activation energies for site-to-site oxygen ion 
transfer, with an improved (decreased) polarization voltage drop across 
the electrolyte at substantially-reduced operating temperatures than are 
required for the operation of state-of-the-art yttria-stabilized zirconia 
solid electrolyte fuel cells. 
With further reference to the drawings, FIG. 1 is an illustration of a 
representative solid electrolyte fuel cell with the components mounted 
vertically in a stack array. Details regarding the electrical 
interconnections and gas manifolding for the cell are conventional and not 
illustrated. For the cell 10, cathode and anode housings 12 and 14 house 
the electrodes and are typically constructed of stainless steel. An oxygen 
containing gas is introduced into the cathode housing 12 by line 16 while 
line 18 serves as a means for introducing hydrogen as a gaseous fuel to 
the anode housing 14. Lines 20 and 22 serve as the means for removing the 
spent oxidant and fuel, respectively. Cell member 24 constitutes the 
molten carbonate electrolyte or a solid oxide electrolyte as described 
herein with opposite surfaces adjacent the electrodes. The lips of the 
anode and cathode cell housings are aluminized in the seal areas to 
provide rectifying contact and blockage of short-circuiting currents 
between cell housings through the electrolyte. 
The following examples are provided to illustrate some embodiments of the 
invention and are not intended to be limiting with respect to the scope of 
the invention. 
EXAMPLE I 
In the preparation of a molten carbonate fuel cell whose performance is 
illustrated in FIG. 3, a surface of a preoxidized nickel cathode was 
spray-coated with an aqueous slurry of Ni/NiAl.sub.2 O.sub.4. After 
drying, the coating weighed approximately 0.88 g. 
In the preparation of a nickel spinel, Ni/NiAl.sub.2 O.sub.4 was prepared 
from high surface gamma-alumina. About 294 g of Al.sub.2 O.sub.3 was 
combined with about 839 g of Ni(NO.sub.3).sub.2 and about 480 g of water 
to form a slurry. The slurry was placed in a two-liter flask and heated to 
about 260.degree. C. to produce gray-black chunks of material which were 
ground into a powder. The powder was reheated to about 1600.degree. C. in 
air for about two hours to complete the reaction and distribute the nickel 
into the lattice structure of the composition NiAl.sub.2 O.sub.4, a nickel 
spinel. Subsequently the composition was partially reduced with flowing 
hydrogen at about 650.degree. C. for about 97 hours. X-ray diffraction 
showed the presence of metallic nickel. The composition is hereinafter 
described as Ni/NiAl.sub.2 O.sub.4. 
A 50 wt. % suspension of Ni/NiAl.sub.2 O.sub.4 in 1% aqueous ammonium 
alginate solution was ball milled for about 8 hours and then further 
diluted with an equal volume of water to provide a suitable spraying 
consistency and decomposable binder for the dried coating. After trial 
spraying showed that some smooth non-dusting surface coats could be 
applied to preoxidized cathode surfaces with penetration extending no 
further than the surface macropores (10-15 .mu.m), the Ni/NiAl.sub.2 
O.sub.4 slurry was spray-coated onto the preoxidized nickel oxide cathode. 
A test cell was constructed with an electrolyte tile composed of about 48 g 
of 64 wt. % of a molten carbonate eutectic with the remainder being solid 
lithium aluminate (LiAlO.sub.2) powder particles having a surface area of 
about 33 m.sup.2 /g tile was about 4.375 inches.times.4.375 inches.times.2 
mm. In the assembly of the cell, a perforated sheet metal current 
collector was laid in the frame of the stainless steel anode housing, 
followed by the porous Ni/Cr anode, the tile, the pretreated nickel oxide 
cathode with its spray-coated face adjacent the tile, a second current 
collector, and the cathode housing member. The assembly with electrical 
connections to a variable load and fuel and oxidant connections was placed 
in an oven and heated to about 650.degree. C. under about 10 psi pressure 
to form an edge-seal at the tile perimeter oversized with respect to the 
electrodes. Approximately twelve hours were required to form the gas seal. 
In this conditioning, the extremely reactive nickel metal portion of the 
Ni/NiAl.sub.4 O.sub.4 thin layer or coating on the cathode was quickly 
corroded by the molten carbonate and provided a ready source of nickel ion 
which migrated into the electrolyte tile and formed nickel components on 
the particulate LiAlO.sub.2 surfaces of the tile. 
In the test of the cell, a constant current of about 80 ma/cm.sup.2 was 
applied to the cell and its voltage was measured. FIG. 3 includes 
performance data for several molten carbonate cells including the 
performance of a series of coated-electrode cells with the baseline 
performance of an untreated "standard" cell, SQ-20. Tests SQ-21, SQ-23, 
SQ-24, SQ-27, SQ-28, and SQ-29 were based on cells where lithium aluminate 
spray-coatings were incorporated on the anode at the anode-tile interface 
in an effort to reduce hydrogen cross-over during cell operation. Tests 
for cell SQ-25, the cell of this invention, and six months later, for 
SQ-32, its duplicate in construction and performance, incorporated the 
partially-reduced nickel aluminate Ni/NiAl.sub.2 O.sub.4 at the 
cathode-tile interface, showed essentially equal effectiveness in reducing 
hydrogen cross-over and in addition were shown to have the earliest rise 
to plateau performance. For both cells the voltage reached 0.7 volts 
within 15-25 hours, and continued at 0.7-0.72 volts for past 200 hours. At 
the initial time period of 15-25 hours, other cells developed voltages 
below 0.7 volts and required up to 250 hours to reach their plateau 
voltages. 
This early increase in cell potential was found to be independent of ohmic 
cell resistance, which for cell SQ-32 was measured by current-interrupt 
techniques and was found to be constant over the test-life of the cell. 
The improvement in cell potential rising to a plateau was attributed to a 
reduction in the polarization processes, particularly to an improvement in 
oxygen-ion transport, on surfaces of the solid dispersed in the tile body 
itself, in the regions near the cathode-tile interface. This improvement 
was further attributed to the improvement in the oxygen ion transport 
performance of the electrolyte tile apart from the spinel structure and 
the cathode. Based on the performance of the cell, the spinel structure 
did not appear to be functioning as an extended cathode nor as the primary 
electrolyte but as a readily accessible source of nickel for the 
electrolyte tile by which the nickel could be transferred to the 
electrolyte tile within a reasonably short time and the oxygen ion 
transfer of the tile could be enhanced. 
EXAMPLE II 
In the preparation of a solid electrolyte fuel cell, an epsilon-MnO.sub.2 
was measured by nitrogen adsorption/desorption isotherm techniques and was 
found to have a porosity with peak distributions at 8, 20 and 40 .ANG. as 
shown in FIG. 2 illustrating the pore size distribution of a sample of 
MnO.sub.2 It is ground to a free-flowing powder and formed into a paste 
with about 10 g. of 50 wt. % Mn(NO.sub.3).sub.2 and 65 g. of the 
MnO.sub.2. The paste is spread on an aluminum foil, and spread between 
spacer-guides to a form about 4 and 3/8 inches.times.4 and 3/8 inches 
.times. 0.07 inches, and overlaid with a second aluminum foil and slowly 
heated to about 350.degree. C. in a lightly-loaded platten press. The 
manganous nitrate decomposes to form a (porous) cement of beta-MnO.sub.2 
which binds the epsilon phase into an electrolyte slab. Repeated 
impregnation and decomposition in the press yield a gas-impervious 
electrolyte slab of controlled dimensions. 
Electrode attachment is obtained utilizing dead-weight loaded quartz plates 
rather than the platten press, and cementing the anode and the fragile 
lithiated, preoxidized NiO plaques to either side of the electrolyte slab 
with aqueous manganous nitrate solution, again employing Al foil release 
sheets, decomposing the nitrate in a ventilated air oven at 350.degree. C. 
The assembly less the quartz plates and aluminum foil pieces is mounted in 
a conventional molten carbonate fuel cell housing. In the assembly, the 
electrolyte slab extends beyond the anode and cathode, and combined with 
the upper and lower housing members, forms seals for the cell. The cell is 
tested with oxygen and hydrogen at about 500.degree.-600.degree. C. at a 
constant current of about 200 ma/cm.sup.2. A voltage in the order of about 
0.5-0.9 V is obtained. 
As described herein, the invention provides electrochemical cells with 
enhanced performance. For the molten carbonate cell, the initial 
conditioning of the cell is reduced. In a solid electrolyte cell, the 
combination of small open pores and transition metal oxide in the 
surrounding composition will permit operation at reduced temperatures.