Solid electrolyte electrochemical cell

A new type of electrochemical cell which can be used for generating electricity or in an electrolysis mode for producing gases such as hydrogen and oxygen comprises laterally spaced apart or side-by-side catalyst layers as electrodes with the gap between the catalyst layers being bridged by a solid electrolyte which provides an ion conductive path from one catalyst layer to the other. The catalyst layers and the electrolyte are preferably in the form of thin films or layers on the surface of an inert supporting substrate. A plurality of these cells may be disposed on the substrate and interconnected electrically forming a network of series and parallel connected cells. Means are provided to feed fuel and oxidant to the electrodes either as separate gases or mixed together if appropriate catalytic materials are selected.

DESCRIPTION 
1. TECHNICAL FIELD 
The present invention relates to electrochemical cells, and, more 
particularly to electrochemical cells of simplified construction which 
utilize a solid electrolyte. 
2. BACKGROUND ART 
Electrochemical cells such as fuel cells are very old in the art. The basic 
components of an electrochemical cell are an anode electrode, a cathode 
electrode and an electrolyte. Using the fuel cell as an example, in the 
more conventional type fuel cell each electrode is a self-supporting sheet 
of electrically conducting material which includes a layer of catalytic 
material on one surface thereof or perhaps a catalytic material is 
distributed throughout the sheet. The surface of the anode and cathode 
electrode having the catalyst layer disposed thereon (or either surface if 
the electrode simply includes catalysts dispersed throughout) are arranged 
facing each other with the electrolyte disposed therebetween. The 
electrolyte may simply be a circulating liquid filling the space between 
the facing surfaces of the electrodes, or the liquid electrolyte may be 
disposed in a porous, nonelectrically conductive matrix which is 
sandwiched between the two electrodes. An example of the former type of 
fuel cell configuration is described in commonly owned U.S. Pat. No. 
3,253,953. The latter type of cell is represented by commonly owned U.S. 
Pat. Nos. 4,017,664 and 4,129,685. 
The electrolytes used in these types of cells may be either base 
electrolytes such as potassium hydroxide or acid electrolytes such as 
phosphoric acid. Other electrolytes which have been used are molten 
carbonate electrolytes, which are solid at room temperatures and liquid or 
molten at cell operating temperatures and materials (such as 
borophosphoric acid) which are gels at room temperature and at operating 
temperatures; For the most part, presently known good electrolytes of the 
types just described are very corrosive at cell operating temperatures, 
which severely limit the materials which can be used for other cell 
components. 
Electrolytes which are solid at high temperatures have also been proposed 
and tested. They are described in detail in the book "Solid 
Electrolytes--General Principles, Characterization, Materials, 
Applications" edited by P. Hagenmuller and W. Van Gool, Academia Press, 
N.Y. (1978). One such electrolyte is doped zirconia ceramic. Zirconia is 
thermally and chemically stable at high temperatures and is not corrosive 
like many acid and base electrolytes. The book teaches that at 
temperatures greater than about 700.degree. C. zirconia has excellent 
oxygen ion conductivity. 
This same book also describes, at pages 447 and 448, a "thin-film" fuel 
cell concept, wherein a cell is constructed by overlaying, onto a porous 
substrate, a film of cathode catalyst material, followed by a film of 
doped zirconia electrolyte, followed by a film of anode catalyst material. 
Each film is stated as being 30-100 micrometers thick, forming a 
conventional sandwich type structure (with electrolyte in the middle) 
between 90-300 micrometers thick. The cell operates by feeding a gaseous 
fuel directly to the anode and by feeding the oxidant to the cathode 
catalyst layer through the porous substrate. As with other prior art 
cells, the electrolyte serves as a gas barrier between the oxidant on one 
side of the cell and the fuel on the other side. The requirement that the 
electrolyte be a gas barrier also severely restricts the materials which 
can be used as the electrolyte. 
DISCLOSURE OF THE INVENTION 
One object of the present invention is an electrochemical cell stack of 
simplified construction. 
An additional object of the present invention is a fuel cell which is 
operable on an oxidant and fuel reactant gas mixture. 
Another object of the present invention is an improved cell utilizing a 
solid electrolyte. 
Yet another object of the present invention is an electrochemical cell 
which is operable efficiently at low temperatures. 
Another object of the present invention is an electrochemical cell 
configuration suitable for high speed production methods. 
According to one aspect of the present invention an electrochemical cell 
comprises thin, laterally spaced apart anode and cathode catalyst layers 
in close proximity to each other with a solid electrolyte bridging the gap 
between the catalyst layers to provide an ion conductive path from one 
layer to the other. Another aspect of the present invention is a plurality 
of these cells laterally disposed relative to each other and connected 
electrically in series. 
As used in the foregoing statement of the invention and in the remainder of 
the specification and claims, "laterally" means "to the side" such that 
elements "laterally spaced apart" or "laterally disposed relative to one 
another" do not have surfaces (other than edge surfaces) facing one 
another. 
One important feature of the present invention is the lateral spacing of 
the catalyst layers of each cell with the solid electrolyte 
interconnection between these layers such that ion conduction between the 
catalyst layers is substantially parallel to the surfaces of the catalyst 
layers. This is in contrast to all known prior art cells wherein the 
electrodes have their catalyst surfaces facing each other with the 
electrolyte disposed therebetween forming a sandwich-like structure; and 
ion conduction between electrodes is substantially perpendicular to the 
surfaces of the catalyst layers. 
In one exemplary embodiment the cell components are thin layers of 
appropriate materials. For example, the electrolyte may be a thin layer of 
solid material disposed on a supporting inert substrate, and the catalyst 
layers (i.e., electrodes) may be thin layers of catalytic material applied 
to the surface of the electrolyte layer with a small gap between adjacent 
edges of the catalyst layers. Appropriate means are provided to feed 
reactant gases to the catalyst layers. An electrochemical reaction then 
occurs where each catalyst layer contacts the electrolyte layer; and ions 
of a suitable species are formed and are conducted via the electrolyte 
layer across the gap between the catalyst layers while electrons are 
released and flow from one catalyst layer to the other via a suitable 
external electrical interconnection. 
With the anode and cathode catalyst on the "same side" of the cell, the 
role of the electrolyte as reactant gas barrier between the fuel and 
oxidant is eliminated by the present invention. This may permit the use of 
some materials as electrolyte which otherwise would be unsuitable. 
Furthermore, this permits (although it does not require) the use of 
extremely thin and perhaps even monolayer electrolyte films. 
In this description of the invention and in the appended claims the phrase 
"solid electrolyte" is used in its broadest sense to include any 
electrolyte which exhibits the mechanical properties of a solid as opposed 
to a liquid. In other words, "solid" means a material which retains its 
shape without the benefit of a container or a porous supporting matrix. 
It, therefore, includes materials which are generally considered gels. 
Also, a material may still be considered a solid electrolyte even if its 
mechanism of ion conduction is through a liquid medium or is aided by a 
liquid medium disposed on its surface or within its pores. 
For best efficiency cells of small dimensions are preferred with catalyst 
layers having projected surface areas on the order of a square centimeter 
or less and most preferably even orders of magnitude smaller. The gaps 
between anode and cathode catalyst layers of a cell are also, preferably, 
correspondingly small. The idea is to minimize cell resistance losses by 
reducing the distance the ions must travel. The low cell resistance 
resulting from the small cell dimensions expands the number of materials 
which may be suitable as solid electrolytes. Along these same lines, 
electrolytes which had sufficient ionic conductivity only at very high 
temperatures in prior art cell constructions, may have adequate ionic 
conductivity at much lower temperatures when used in accordance with the 
teachings of the present invention, thereby further opening up the field 
of candidate electrolyte materials. 
From the foregoing it is apparent that a cell of the present invention is 
intended to produce only a small current, perhaps measured in microamps. 
High voltage and power output is obtained by connecting a large number of 
cells in series to form a group of cells, with the cells laterally 
disposed relative to each other on a common supporting surface. A large 
supporting surface, such as a thin wafer, could accommodate many groups of 
series connected cells; and the groups may be electrically connected in 
parallel and series to form a cell stack which further multiplies the 
power output. These wafers may be stacked together and electrically 
interconnected to form a cell stack capable of producing virtually any 
desired power output. Photolithographic thin film technology as used in 
the semiconductor integrated circuit art, is contemplated as being usable 
in the manufacture of cells, cell-groups and cell stacks according to the 
present invention. 
If the individual cells of a cell stack are large enough, manifolding means 
could be provided to feed the cathodes with an oxidant such as air and the 
anodes with a fuel such as hydrogen, keeping the two reactants separate 
from each other as in conventional cells. If the individual cells in a 
network of series and parallel connected cells are very small, it may not 
be physically possible or practical to keep the fuel and oxidant separate 
over the individual anode and cathode catalyst layers. In that case the 
fuel and oxidant would be fed as a mixture over the catalyst layers of all 
the cells. It may be that the reactants would have to be diluted to 
prevent autoignition in the presence of the catalysts; or, instead, the 
catalysts may be appropriately selective to the oxidation of hydrogen or 
to the reduction of oxygen. 
It is contemplated that cells of the present invention may be operable on 
fuels other than hydrogen (e.g., alcohols, hydrocarbons, and the like) and 
oxidants other than oxygen (e.g., halogens, peroxides, oxides of nitrogen, 
and the like). Cells of the present invention may also be operated in the 
regenerative mode to accomplish energy storage.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIGS. 1 and 2 show a "mixed reactant" type fuel cell in accordance with an 
exemplary embodiment of the present invention. In a mixed reactant type 
cell, the fuel, such as hydrogen, and the oxidant, such as oxygen in the 
form of air, are mixed together and the mixture is fed to both the anode 
and cathode of the cell simultaneously via a common reactant gas space 
over the electrodes. 
Referring to FIG. 1, a cell assembly 10 comprises a supporting plate 12 
having a flat top surface 14. Disposed on and adhered to the surface 14 is 
a fuel cell 15 comprising a thin layer of solid electrolyte 16, and anode 
electrode 18, and a cathode electrode 20. The anode and cathode electrodes 
are disposed on and adhered to the surface of the electrolyte layer 16. 
The anode electrode 18 is simply a thin, gas porous, electrically 
conductive anode catalyst layer 22, and the cathode electrode 20 is simply 
a thin, gas porous, electrically conductive cathode catalyst layer 24. The 
anode and cathode catalyst layers are laterally spaced apart in close 
proximity to each other with a gap 26 being defined between the layers. A 
thin electrically conductive layer 28 of metal paint is disposed along an 
edge of each catalyst layer 22, 24. Each electrically conductive layer 28 
also includes fingers 30 of electrically conducting material extending 
over the surface of the catalyst layer and a narrow stripe 31 of 
electrically conducting material extending from the catalyst layer to the 
edge of the support plate 12. An external circuit 32 (shown dotted) 
including a load 33, electrically interconnects the two electrodes. A 
cover plate 34 mates with the top surface 14 of the support plate 12; and 
a cutout 36 in the bottom surface 38 of the cover plate defines a reactant 
gas space 40 (see FIG. 2) over the electrodes 18, 20. The cover plate 34 
also includes a reactant gas inlet channel 42 and a reactant gas outlet 
channel 44, both in communication with the gas space 40. 
FIG. 2 is a cross section through the cell assembly 10 of FIG. 1 with the 
electrolyte layer 16, the catalyst layers 22, 24, and the electrically 
conductive layers 28 drawn with greatly increased thickness for the 
purpose of clarity. In actuality these layers are like very thin layers of 
paint and may only be several micrometers thick, as will be hereinafter 
further described. 
In operation the reactant gas mixture is passed through the cell assembly 
10 in contact with the electrodes 18, 20, via the inlet channel 42, the 
gas space 40, and the outlet channel 44. Assuming that the electrolyte 
material is a proton conductor (although this need not be the case), at 
the anode electrode the fuel in the mixture (e.g., hydrogen) passes into 
the anode catalyst layer 18 and reacts electrochemically in the presence 
of the catalyst and electrolyte thereby generating electrons, protons, and 
heat. The electrons are conducted away from the anode electrode by the 
electrically conductive layer 28, and are conducted to the cathode 
electrode 20 via the external circuit 32. The ions are conducted to the 
cathode electrode 20 by the electrolyte layer 16 which provides an ion 
conductive path between the catalyst layers by bridging the gap 26 
therebetween. At the cathode electrode 20 the oxidant in the reactant gas 
mixture (e.g., oxygen) electrochemically reacts with the ions and 
electrons from the anode electrode to produce water which leaves the cell 
as a vapor with the spent reactant gases via the outlet channel 44, the 
electron flow from one electrode to the other through the external circuit 
32, is the useful electrical energy generated by the cell 15. 
One advantage of the present invention, and the most obvious physical 
difference between the prior art and cells of the present invention, is 
that the anode and cathode electrodes are side by side with the 
electrolyte bridging the gap between adjacent electrode edges, rather than 
the electrodes being face to face with the electrolyte filling the volume 
between opposing surfaces of the electrode and acting as a reactant gas 
separator or barrier. The electrolyte in the present invention is truly 
only an ion conductor between the electrodes since its role as a reactant 
gas separator has been eliminated. This is also the case even if separate 
fuel and oxidant reactants are provided to the anode electrode and cathode 
electrode, as shown in other embodiments hereinafter to be described. 
Another important feature and advantage of the present invention is the 
elimination of a "functional" substrate for the catalyst layers. In most 
cells of the prior art the catalyst layers of at least one and sometimes 
both electrodes are adhered to one side of a gas porous substrate. A 
reactant gas is fed to the other side of the substrate and must pass 
through it to react with the catalyst layer and the electrolyte. In prior 
art cells using a liquid electrolyte there is the further complication of 
electrode flooding which requires the catalyst layer and perhaps the 
substrate to include wetproofing material, such as 
polytetrafluoroethylene. The result, in any case, is reduced effective 
surface area of the catalysts and increased difficulty in bringing the 
reactant gas into contact with both the catalyst and the electrolyte to 
effect the electrochemical reaction. These problems are eliminated by the 
present invention which uses a solid electrolyte, no wetproofing, and no 
porous catalyst supports. While the book "Solid Electrolytes" by 
Hagenmuller et al referred to above describes, on pages 442 and 443, a 
solid electrolyte "sandwich" type cell with similar advantages, that cell 
is limited to a tubular configuration, which is an undesirable restriction 
and, more importantly, requires a structurally self-supporting electrolyte 
element which also must serve as a gas barrier. 
One of the basic ideas behind the cell of the present invention is to 
minimize cell resistance and maximize catalyst effectiveness in a manner 
consistent with the ultimate objective (from a commercial point of view) 
of manufacturing a cost effective fuel cell stack having a useful power 
output. Reducing cell resistance is accomplished, in part, by minimizing 
the gap 26 between the electrodes, thereby reducing the distance the ions 
must travel to effect the electrochemical reaction. This makes the job of 
the electrolyte easier and permits the use of some materials as 
electrolytes which otherwise would not be considered to have sufficient 
ionic conductivity to be useful in fuel cells. In the alternative, some 
electrolytes which were only thought to have sufficiently high ion 
conductivity at high temperatures (e.g., zirconia at 700.degree. C. and 
above) might now have sufficiently high ionic conductivity to be an 
effective fuel cell electrolyte at much lower temperatures and perhaps 
even at room temperature. 
The present invention provides a unique opportunity to employ electrolytes 
which conduct primarily by surface ion conduction as opposed to the normal 
bulk ionic conduction. This is made possible by relieving the electrolyte 
of the gas separation requirement thus allowing the surface of a solid to 
interconnect the two electrodes. Ionic conduction in cells of the present 
invention is, however, not limited to surface ion conduction. Examples 
disclosed in this application may, in fact, function partially by bulk and 
partially by surface ionic conduction. It is not required that the exact 
type of conduction be known in order to practice this invention. 
In the exemplary embodiment of FIGS. 1 & 2, the electrolyte is in the form 
of a thin layer. In that embodiment (and other embodiments using thin 
layers of electrolyte) it is preferred that the electrolyte layer be no 
greater than about 50 micrometers thick and most preferably less than 10 
micrometers thick. It is not presently known what the lower limit of 
thickness is such that satisfactory ion conduction is still obtained. 
Satisfactory performance has been obtained with layers measured to be 
about 3 micrometers thick. 
Notwithstanding the foregoing, a thick electrolyte layer, even thick enough 
to be self-supporting, could also be used in the present invention, but 
would not be expected to provide any improvement in cell performance (as 
compared to a thin film electrolyte) and is likely to be wasteful of 
material. 
We have tested Baymal.RTM. alumina (a fibrillar boehmite alumina formerly 
manufactured by E. I. DuPont and more fully described in U.S. Pat. No. 
2,915,475) as an electrolyte in fuel cells of the present invention and 
found it to work satisfactorily. Other materials which might make suitable 
electrolytes for use in the present invention are: hydronium .beta." 
alumina, hydrogen uranyl phosphate, phosphomolybdic acid, and 
phosphotungstic acid. These other materials have been recently reported in 
the literature as being highly ion conductive in the solid state. 
Additional possible electrolyte materials are silica gel, alumina gel or 
the like. 
Turning now to the electrodes, if the fuel and oxidant are separately 
manifolded to the anode and cathode electrodes, respectively, a 
conventional, electrically conductive fuel cell anode and cathode 
catalytic material, such as platinum or supported platinum, may be used 
for both catalyst layers. On the other hand, if mixed reactants are used, 
such as is the case in the embodiments shown in FIGS. 1 and 2, something 
must be done to cause an electrical potential to exist between the 
electrodes. For example, "selective" catalysts may be used for one or both 
electrodes. In this application a selective catalyst is one which, in the 
presence of mixed fuel and oxidant, will favor, to a significant extent, 
either the anode or cathode electrochemical reaction. Furthermore, as 
herein defined, to prevent ignition of the reactant mixture, a selective 
catalyst does not contribute to the direct chemical combination of the 
reactants. 
Whether conventional or selective catalysts are utilized, it is preferred 
(although not required) that the catalyst layer be an intimate mixture of 
the catalytic material and the electrolyte material. This brings the 
electrolyte material and the catalyst material into intimate contact 
thereby improving the catalyst/electrolyte/reactant gas interaction during 
cell operation. The electrolyte may also serve as a binder for the 
catalyst layer. Some catalysts which may be used to selectively reduce 
oxygen are: strontium ruthenate (SrRuO.sub.3) and lanthanum manganate 
(LaMnO.sub.3). A catalyst which is selective to the oxidation of hydrogen 
is lanthanum cobalt ruthenate [La(CO.sub.0.5 Ru.sub.0.5)O.sub.3 ]. 
Alternatively, a catalyst layer can be covered with a film or layer or 
material which is selective to (i.e., favors) the diffusion therethrough 
of the particular gas to be reacted at the electrode. A selective 
diffusion layer of this type does not have to be 100% selective to be 
effective. In other words, it does not have to completely exclude the 
other gases in the mixture. For example, some materials known to be 
selective to the diffusion of hydrogen are: nylon, polysulfone, 
polytrifluorochloroethylene and polyproplene. 
A fuel cell like that shown in FIGS. 1 and 2 was built and tested. The 
support plate 12 and the cover plate 34 were made from 3.2 mm thick 
acrylic sheet. The electrolyte layer 16 was made from a fine powder of 
Baymal alumina. This fine powder disperses readily in water to form a 
colloidal dispersion. In this example we made a dispersion. In this 
example we made a dispersion comprising 5%, by weight, Baymal alumina in 
water. Using a small brush a film of this dispersion was applied to the 
surface 14 and was immediately exposed to ammonia vapor which caused the 
film to gel. This gel was allowed to dry at room temperature resulting in 
a solid film having a typical thickness of about 3.0 micrometers. 
The catalyst layers 22, 24 were applied to the electrolyte layer 16 in such 
a manner that a long edge of one layer was parallel to a long edge of the 
other layer with a gap 26 therebetween on only 0.3-0.4 millimeter. The 
anode catalyst layer 22 was prepared by dispersing 1.0 gm platinum 
supported on carbon (a conventional fuel cell catalyst) and 0.5 gm Baymal 
alumina in 9.5 gm water. The solids were allowed to settle out for several 
hours and the clear liquid was decanted. The remaining wet paste, which 
had a consistency of poster paint, was painted onto the electrolyte layer 
16 as a rectangle about 2.0 cm long, 0.5 cm wide and 5 micrometers thick 
(after drying). The finished anode catalyst layer was an intimate mixture 
of supported platinum and Baymal alumina electrolyte. 
The cathode catalyst layer was prepared by dispersing 0.45 g strontium 
ruthenate in 30 ml of a 5% (by weight) aqueous solution of Baymal alumina. 
The solids were allowed to settle out for several hours and the clear 
liquid was decanted. The remaining wet paste was painted onto the 
electrolyte layer 16 as a rectangle 2.0 cm long, 0.5 cm wide, and 5 
micrometers thick (after drying). The finished cathode catalyst layer was 
an intimate mixture of strontium ruthenate and Baymal alumina electrolyte. 
Strontium ruthenate was chosen as the cathode catalyst because tests showed 
it to be selective to the reduction of oxygen. The selective catalytic 
performance of strontium ruthenate was determined by comparing it to the 
catalytic performance of a platinum catalyst layer in a cell of the type 
just described, except that the hydrogen and oxygen reactant gases over 
the catalyst layers were kept separate by suitable barrier means. First 
the strontium ruthenate was tested as a cathode by feeding 100% oxygen to 
it while feeding 100% hydrogen to the supported platinum catalyst layer. 
The curve A in the graph of FIG. 12 shows voltage versus current for 
varying resistive loads with strontium ruthenate as the cathode. The 
reactant flows were then reversed such that the strontium ruthenate was 
the anode. Curve B in FIG. 12 shows voltage versus current for varying 
resistive loads with strontium ruthenate as the anode. From the graph it 
can clearly be seen that strontium ruthenate has a significantly higher 
degree of catalytic activity as a cathode for the reduction of oxygen than 
it has as an anode for the oxidation of hydrogen. 
The electrically conductive layer 28 was silver paint of the type generally 
used on printed circuit boards. It, too, was applied by hand using a small 
brush. The layer had a typical thickness of about 10 micrometers. It is 
estimated that the layer 28, including the fingers 30, covered about 
10-15% of the surface area of each electrode. It is believed that this did 
not have a serious effect on cell performance. Note, however, that care 
must be taken not to cover too much of the catalyst surface area to assure 
that reactant gases have essentially complete access to catalyst areas. 
To prevent reactant gas from leaking from the gas space 40 between the 
mating faces of the plates 12, 34, a thin layer of Fluorolube.RTM. grease 
(a fluorocarbon-based product having the consistency of petroleum jelly 
and manufactured by Hooker Chemical Corp.) was applied to the mating 
surfaces surrounding the electrolyte layer 16. Clamps were used to hold 
the plates in gas sealing relationship during the tests hereinafter 
described. 
The foregoing cell was run at room temperature on a reactant gas mixture 
comprising air and an equal amount (by volume) of 4% hydrogen in nitrogen. 
A diluted fuel gas was used to ensure the gas mixture could not ignite 
during the test. The reactant gas mixture was humidified to the extent of 
room temperature saturation prior to passing it through the cell by 
bubbling it through some water. It is believed that the surface ion 
conduction hereinbefore referred to takes the form of hydronium ion 
(H.sub.3 O.sup.+) migration, and the water vapor enhances the ion current 
flow through the cell by combining with the hydrogen ions to form 
hydronium ions at the anode catalyst/electrolyte interface. The flow rate 
through the cell was maintained substantially constant at about 15 ml per 
minute. The results of the test, which continued for about 3 days, is 
displayed in Table 1 below. It took the cell about an hour to stabilize at 
an open circuit voltage of about 0.67 volts, and results prior to this 
time are not reflected in the table. 
TABLE 1 
______________________________________ 
Resistance Voltage Current 
(10000 .OMEGA.) 
(volts) (microamps) 
______________________________________ 
1000. 0.507 0.51 
470. 0.388 0.82 
100. 0.166 1.66 
47. 0.089 1.89 
15. 0.031 2.1 
10. 0.023 2.3 
4.7 0.010 2.1 
1.0 0.003 3.0 
______________________________________ 
From Table 1 it is clear that a measurable amount of power was produced by 
the test cell despite the fact that only the cathode was a selective 
catalyst. 
FIGS. 3 thru 5 show yet another embodiment of the present invention. The 
drawing depicts a cell-group assembly 99 comprising a cell stack component 
100 and reactant manifold means 101. The cell stack component 100 
comprises a "cell-group" of five cells labeled 102A thru 102E and a 
self-supporting substrate or support plate 104. A cell-group is a 
plurality of cells laterally disposed relative to each other and connected 
electrically in series. The manifold means 101 comprises a manifold plate 
105 and a top plate 106. The five cells 102A thru 102E are disposed on the 
flat top surface 107 of the support plate 104. Each of the cells is 
similar in construction to the cell described with respect to FIGS. 1 and 
2. Thus, referring to FIG. 3, each cell comprises an electrolyte layer 
108, an anode catalyst layer 110, and a cathode catalyst layer 112. The 
catalyst layers within each cell are laterally spaced apart and in close 
proximity to each other on the surface of their respective electrolyte 
layers 108. A gap 114 separates the catalyst layers within a cell. Each 
cell 102A thru 102E is adjacent at least one other of the cells such that 
the cathode catalyst layer of one cell of each adjacent pair is in close 
proximity to but laterally spaced from the anode catalyst layer of the 
other cell of that pair. A space 116 (approximately the same width as the 
gap 114) is shown in the drawing as separating these catalyst layers. Gaps 
118 separate the electrolyte layers 108 of adjacent cells to prevent ionic 
short circuits. The cells 102A thru 102E are connected electrically in 
series by bridging the spaces 116 with a layer 120 of electrically 
conductive material. 
The spacial relationship between the various layers is best seen in FIG. 3A 
taken in the direction A of FIG. 3 wherein the thicknesses of the various 
cell layers are exaggerated for clarity. Note that each layer 120 includes 
a narrow stripe 121 of material under the adjacent catalyst edges and is 
somewhat wider than the gap between the catalyst edges. The stripes 121 
are narrower than the gaps 118 such that the stripes 121 do not provide 
any electrical interconnection between adjacent electrolyte layers 108. A 
plurality of fingers 122 extend over the surfaces of the catalyst layers 
and interconnect with the stripes 121 along the gaps 116 for the purpose 
of providing improved electrical communication between the cells. The 
electrically conductive layers 120 of end cells 102A and 102E each include 
a narrow stripe 124 of electrically conductive material leading to an edge 
of the plate 104. These stripes 124 are interconnected by an external 
circuit 126 which includes a load 128. 
Referring to FIGS. 4 and 5, machined into the bottom surface 130 of the 
manifold plate 105 is a fuel manifold channel 131 with a plurality of 
individual fuel channels 132 extending perpendicularly therefrom over each 
anode catalyst layer 110. A cylindrical fuel inlet passage 133 (FIG. 3 and 
FIG. 5) passes upwardly through both the plates 105 and 106 and 
communicates with the right-hand end of the fuel manifold channel 131. 
Also machined into the bottom surface 130 of the plate 105 is an oxidant 
manifold channel 134 with a plurality of individual oxidant channels 136 
extending perpendicularly therefrom over each cathode catalyst layer 112. 
A cylindrical oxidant inlet passage 137 (FIG. 3 and FIG. 5) passes 
upwardly through both the plates 105 and 106 and communicates with the 
right-hand end of the oxidant manifold channel 134. The individual fuel 
channels 132 define separate fuel gas spaces 138 over each anode catalyst 
layer; and the individual oxidant channels 136 define separate oxidant gas 
spaces 140 over each cathode catalyst layer. Walls 141 in the plate 105 
separate adjacent fuel and oxidant gas spaces and extend, alternately, 
along the gaps 114, 116 in sealing contact with the surfaces of the 
electrolyte layers 108 and the electrically conductive layers 120, 
respectively. 
Associated with the individual fuel gas spaces 138, is a common fuel 
exhaust manifold channel 142 machined into the top surface 144 of the 
manifold plate 105. Cell fuel exhaust holes 146 drilled through the 
manifold plate 105 have their inlet ends 148 opening into their respective 
fuel gas spaces 138 and their outlet ends 150 opening into the exhaust 
manifold channel 142. Similarly, an oxidant exhaust manifold channel 152 
(FIG. 3) in the top surface 144 of the manifold plate 105 communicates 
with the individual oxidant gas spaces 140 via cell oxidant exhaust holes 
154 (FIG. 3) through the manifold plate 105. A cylindrical fuel outlet 
passage 156 and oxidant outlet passage 158 drilled through the top plate 
106 communicate, respectively, with the left-hand end of the fuel exhaust 
manifold channel 142 and oxidant exhaust manifold channel 152. The three 
plates (shown in assembled relationship in the offset cross section of 
FIG. 4) are secured together by any suitable means such as bolts or 
clamps, not shown. As with the embodiment of FIGS. 1 and 2, a fluorocarbon 
base grease is applied to the mating surfaces of the plates to prevent gas 
leakage from the various manifolds and gas spaces formed between the 
plates. 
A cell stack assembly comprising a five-cell cell-group like that shown in 
FIGS. 3 thru 5 was built and tested. Plates 104, 105, and 106 were made 
from acrylic sheet 3.2 mm thick. The electrolyte layers 108 were made from 
Baymal alumina, the same material as used in the single cell test 
described above and were applied in the same manner. In this example the 
electrolyte layer had an estimated thickness of about 3 micrometers. Its 
area was large enough to accommodate the greater part of both catalyst 
layers hereinafter described. The gap 118 between adjacent electrolyte 
layers was about 3.2 mm wide. After applying the electrolyte layers to the 
support plate a stripe 121 of electrically conductive silver paint 1.5-2.0 
mm wide and about 10 micrometers thick was painted along the gaps 118 
between the electrolyte layers but not touching the electrolyte layers so 
as not to provide an electrical interconnection therebetween. 
Since the fuel and oxidant were kept separated, the same material was used 
for both the anode and cathode catalyst layers 110, 112. In this 
embodiment they were made from the same material (i.e., an intimate 
mixture of Baymal alumina and carbon supported platinum) as the anode 
catalyst layer in the single cell example hereinabove described. The 
catalyst layers were also prepared and applied by the same method as 
described for that previous example. In this cell-group each catalyst 
layer was a rectangle about 8 mm long and 5 mm wide. Its thickness was 
about 5 micrometers. The catalyst layers were applied to the electrolyte 
layers in such a manner that each long edge of each catalyst layer was 
parallel to a long edge of the adjacent catalyst layer, and one edge of 
each catalyst layer overlaid one of the metallic paint stripes 121 which 
had been applied along the gaps between electrolyte layers. Within each 
cell the gap 114 was about 0.4 millimeter. The space 116 between the 
catalyst layers of adjacent cells was also about 0.4 millimeter. The 
silver paint fingers 122 were then painted onto the surface of the 
catalyst layers, interconnecting with the silver paint stripes 121 exposed 
between the catalyst layers. It is estimated that the fingers 122, covered 
about 10% of the surface area of each catalyst layer. 
In a test the foregoing cell stack component was run at room temperature 
using pure hydrogen as the fuel and pure oxygen as the oxidant, both 
humidified to the extent of room temperature saturation. The hydrogen was 
introduced into the cells via the fuel inlet passage 133 at a flow rate of 
about 14 ml per minute, and was distributed to the fuel gas spaces 138 
over the anode catalyst layers 110 via the fuel manifold channel 131. 
Spent fuel left each cell via the exhaust holes 146 leading to the fuel 
exhaust manifold channel 142, and from that channel left the cell stack 
component via the fuel outlet passage 156. Similarly, the oxygen was 
introduced into the cell stack component at a flow rate of about 3 ml per 
minute via the oxidant inlet passage 137, whereupon it was distributed to 
the oxidant gas spaces 140 over the cathode catalyst layers 112. Spent 
oxidant left the cells via the oxidant exhaust holes 154, and exited the 
cell stack component via the oxidant outlet passage 158. 
The results of the test are shown in FIG. 13 as performance curve A. 
A single cell of the same size and configuration as the cells of the 
five-cell cell-group was also tested under the same operating conditions. 
The results of that test are displayed in FIG. 13 as performance curve B. 
A comparison of curves A and B demonstrate the voltage additive effect of 
electrically connecting cells of the present invention in series. 
Turning now to FIGS. 6 and 7, a fuel cell stack 200 is shown. The stack 200 
includes a cell stack component 202, a manifold plate 204, and a top plate 
206. The cell stack component 202 comprises a support plate 208 having 
disposed on the top surface 210 thereof five cell-groups 212 each 
consisting of five cells 214. Each cell-group 212 is identical to the 
five-cell cell-group described with respect to FIGS. 3 thru 5. Reactant 
gas manifolding for feeding and removing reactant gases from each 
cell-group 212 is also very similar to that described with respect to the 
embodiment of FIGS. 3 thru 5. The cell-groups 212 are connected 
electrically in parallel by thin stripes 216, 218 of electrically 
conductive paint, and are connected to an external circuit 220 which 
includes a load 222. 
Referring to FIG. 7 (which is a view taken in the direction C of FIG. 6), 
the bottom surface 224 of the manifold plate 204 includes a main fuel 
manifold channel 225 and a main oxidant manifold channel 226 machined 
therein. Fuel enters the stack 200 via a conduit 227 in communication with 
the main fuel manifold channel 225 via a passageway 228 through the 
manifold plate 204. Oxidant enters the stack 200 via a conduit 229 which 
is in communication with the main oxidant manifold channel 226 via a 
passageway 230 through the plate 204. The main fuel manifold channel 225 
feeds fuel to a plurality of fuel header channels 231 which are 
functionally the same as the channel 131 of FIG. 5. The main oxidant 
manifold channel 226 feeds oxidant to oxidant header channels 232 which 
are functionally the same as the channel 134 of FIG. 5. Each header 
channel 231, 232 is associated with one of the cell-groups 212. Each fuel 
header channel 231 feeds fuel to individual fuel channels 234 which define 
separate fuel gas spaces over the anode catalyst layers of a cell-group 
212. Similarly, oxidant header channels 232 feed oxidant to individual 
oxidant channels 236 which define separate oxidant gas spaces over the 
cathode catalyst layers of a cell-group. Walls 237 act as gas barriers or 
separators between the fuel and oxidant gas spaces. Spent reactant gases 
leave each cell via fuel exhaust holes 238 and oxidant exhaust holes 240 
drilled through the manifold plate 204 and which lead, respectively, to 
fuel exhaust channels 242 and oxidant exhaust channels 244 machined into 
the top surface 246 of the manifold plate 204. The exhaust channels 242, 
244 are functionally the same as the fuel exhaust manifold channel 142 and 
oxidant exhaust manifold channel 152, respectively, of the embodiment of 
FIGS. 3 thru 5. The fuel exhaust channels 242 empty into a fuel exhaust 
header channel 248 and leave the stack via a conduit 250 which is in 
communication with the header channel 248 via a passageway 252. The spent 
oxidant empties into an oxidant exhaust header channel 254 and leaves the 
stack via a conduit 256 which is in communication with the header channel 
254 via a passageway 258. 
A twenty-five cell stack virtually identical to that shown in FIGS. 6 and 7 
was built and tested. Each cell-group and the individual cells therein 
were substantially identical in both materials, size, and method of 
construction as the sngle five-cell cell-group built and tested as 
described above. Test conditions, including reactant gas compositions and 
flow rates, were also the same as for the single five-cell cell-group test 
described above. 
The results of that test are displayed in FIG. 13 as performance curve C. 
The amount of oxygen and hydrogen available to the cells using the same 
flow rates as indicated above for the single five-cell cell-group was 
determined to be well in excess of that required to generate the observed 
current. A comparison with curve A clearly shows the current additive 
effect of connecting cell-groups in parallel. 
Although not shown, it is contemplated that a larger cell stack with 
greater power output could be made by stacking together, one atop the 
other, and electrically interconnecting several stacks 200. 
In the cells of all the foregoing examples the catalyst layers are 
disposed, in major part, on the surface of the electrolyte layer which, in 
turn, is disposed on the surface of a substrate or support plate. FIGS. 8 
thru 11 show two other examples of cell-group configurations considered to 
be within the scope of the present invention. In FIGS. 8 and 9, part of a 
cell-group 300 is shown disposed on a nonconductive, inert support plate 
302. The cell-group 300 is formed by applying narrow stripes or layers 306 
of solid electrolyte to the surface 304 of the support plate, alternating 
with narrow stripes or layers 308 of electrically conductive material. 
Anode catalyst layers 310 and cathode catalyst layers 312 are then applied 
to the surface 304 of the support plate 302. Each catalyst layer is 
applied with one of its long edges 314 overlying a stripe 306 of 
electrolyte material, and its other long edge 316 overlying a stripe 308 
of electrically conductive material. Note that the central portion or each 
catalyst layer is disposed directly on the surface 304. 
In the embodiments of FIGS. 10 and 11, the anode and cathode catalyst 
layers 400, 402, respectively, are applied to the surface 404 of an inert 
support plate 406. Gaps 408 between adjacent catalyst layers are 
alternately bridged by stripes or thin layers of electrolyte material 410 
and electrically conductive material 412. Fingers 414 of electrically 
conductive material extending outwardly from the electrically conductive 
stripes 412 are then applied to the surfaces of the catalyst layers to 
improve electrical conductivity. 
The several embodiments shown in the drawing and described in the 
specification are only exemplary and should not be construed as limiting 
that which the inventors believe to be their invention. It should be 
understood by those skilled in the art that various changes and omissions 
in the form and detail of these embodiments may be made without departing 
from the spirit and the scope of the invention.