Electrochemical fuel cell employing ambient air as the oxidant and coolant

An electrochemical fuel cell assembly includes a membrane electrode assembly which comprises an anode, a cathode having a surface thereof exposed to ambient air, and an ion exchange membrane interposed between the anode and the cathode. A seal forms a gas-impermeable barrier around the anode to which a gaseous fuel stream is supplied. The assembly further includes a thermally conductive plate having a plurality of thermally conductive members or fins extending from a major surface of the plate. The thermally conductive members contact portions of the exposed cathode surface. Adjacent thermally conductive members cooperate with the plate and the exposed cathode surface to form air conducting channels. Heat generated exothermically in the membrane electrode assembly is dissipated to the atmosphere through the thermally conductive members.

FIELD OF THE INVENTION 
This invention relates generally to electrochemical fuel cells and, more 
particularly, to a fuel cell which employs ambient air as both an oxidant 
and a coolant. 
BACKGROUND OF THE INVENTION 
A fuel cell is a device which generates electrical energy by converting 
chemical energy directly into electrical energy by oxidation of fuel 
supplied to the cell. Fuel cells are advantageous because they convert 
chemical energy directly to electrical energy without the necessity of 
undergoing any intermediate steps, for example, combustion of a 
hydrocarbon or carbonaceous fuel as takes place in a thermal power 
station. 
A typical fuel cell includes an anode, a cathode and an electrolyte. Fuel 
and oxidant are supplied to the anode and cathode, respectively. At the 
anode, the fuel permeates the electrode material and reacts with an anode 
catalyst layer to form cations (protons) and electrons. The cations 
migrate through the electrolyte to the cathode. At the cathode, the 
oxygen-containing gas supply reacts with a cathode catalyst layer to form 
anions. The electrons produced at the anode travel from the fuel cell 
anode, through an external load, and back into the cathode of the cell. 
The anions produced at the cathode react with the cations and electrons to 
form a reaction product which is removed from the cell. 
In electrochemical fuel cells employing hydrogen as the fuel and 
oxygen-containing air (or pure oxygen) as the oxidant, a catalyzed 
reaction at the anode produces hydrogen cations from the fuel supply. This 
type of fuel cell is advantageous because the only reaction product is 
water. An ion exchange membrane facilitates the migration of hydrogen 
cations from the anode to the cathode. In addition to conducting hydrogen 
cations, the membrane isolates the hydrogen fuel stream from the oxidant 
stream comprising oxygen containing air. At the cathode, oxygen reacts at 
the catalyst layer to form anions. The anions formed at the cathode react 
with the hydrogen ions that have crossed the membrane to form liquid water 
as the reaction product. The anode and cathode reactions in such fuel 
cells is shown in the following equations: 
EQU Anode reaction: H.sub.2 .fwdarw.2H.sup.+ +2e.sup.- 
EQU Cathode reaction: 1/2O.sub.2 +2 H.sup.+ +2.sup.- .fwdarw. H.sub.2 O 
A type of fuel cell known as a solid polymer fuel cell ("SPFC") contains a 
membrane electrode assembly ("MEA") consisting of a solid polymer 
electrolyte or ion exchange membrane disposed between two electrodes 
formed of porous, electrically conductive sheet material. The electrodes 
are typically formed of carbon fiber paper ("CFP"), and are generally 
impregnated or coated with a hydrophobic polymer, such as 
polytetrafluoroethylene. The MEA contains a layer of catalyst at each 
membrane/electrode interface to induce the desired electrochemical 
reaction. A finely divided platinum catalyst is typically employed. The 
MEA is in turn disposed between two electrically conductive plates, each 
of which has at least one flow passage engraved or milled therein. These 
fluid flow field plates are typically formed of graphite. The flow 
passages direct the fuel and oxidant to the respective electrodes, namely, 
the anode on the fuel side and 10 the cathode on the oxidant side. The 
electrodes are electrically coupled to provide a path for conducting 
electrons between the electrodes. 
In a single cell arrangement, fluid flow field plates are provided on each 
of the anode and cathode sides. The plates act as current collectors, 
provide support for the electrodes, provide access channels for the fuel 
and oxidant to the respective anode and cathode surfaces, and provide 
channels for the removal of water formed during operation of the cell. 
Two or more fuel cells can be connected together in series or in parallel 
to increase the overall power output of the assembly. In such 
arrangements, the cells are typically connected in series, wherein one 
side of a given plate serves as an anode plate for one cell and the other 
side of the plate is the cathode plate for the adjacent cell. Such a 
series connected multiple fuel cell arrangement is referred to as a fuel 
cell stack, and is usually held together by tie rods and end plates. The 
stack typically includes manifolds and inlets for directing the fuel 
(substantially pure hydrogen, methanol reformate or natural gas reformate) 
and the oxidant (substantially pure oxygen or oxygen-containing air) to 
the anode and cathode flow field channels. The stack also usually includes 
a manifold and inlet for directing the coolant fluid, typically water, to 
interior channels within the stack to absorb heat generated by the 
exothermic reaction of hydrogen and oxygen within the fuel cells. The 
stack also generally includes exhaust outlets and manifolds for expelling 
the unreacted fuel and oxidant gases, each carrying entrained water, as 
well as an outlet manifold for the coolant water exiting the stack. 
Conventional fuel cell and stack designs have several inherent 
disadvantages. First, conventional designs typically employ liquid cooling 
systems for regulating the cells' operating temperature. Liquid cooling 
systems are disadvantageous because they require the incorporation of 
additional components to direct coolant into thermal contact with fuel 
cells. The power requirements to operate such additional components, such 
as pumps and cooling fans, represent an additional parasitic load on the 
system, thereby decreasing the net power derivable from the stack. Such 
additional components also add volume, weight, complexity and cost to fuel 
cell designs. 
Second, conventional designs employ further parasitic devices such as pumps 
for the delivery of pressurized fuel and oxidant to the fuel cell. In 
addition to adding volume, weight, complexity and cost, these parasitic 
systems also reduce the overall power efficiency of the system. 
Third, in conventional stack arrangements it is difficult to identify and 
replace defective fuel cells without disrupting the operation of the 
entire fuel cell stack. 
The present invention is directed to circumventing one or more of the 
above-mentioned disadvantages. Other objects and advantages of the 
invention will become apparent upon reading the following detailed 
description and appended claims, and upon reference to the accompanying 
drawings. 
SUMMARY OF THE INVENTION 
The above and other objects are achieved by an electrochemical fuel cell 
assembly comprising: 
(a) a membrane electrode assembly comprising a porous electrically 
conductive anode, a porous electrically conductive cathode having a 
surface thereof exposed to ambient air, and an ion exchange membrane 
interposed between the anode and the cathode; 
(b) sealant means for forming a gas-impermeable barrier around the anode; 
(c) fuel delivery means for supplying a gaseous fuel stream to the anode; 
(d) electrical connection means for providing an electrical connection to 
the anode and to the cathode; and 
(e) a thermally conductive plate having a plurality of first thermally 
conductive members extending from a major surface of the plate, the first 
members contacting portions of the exposed cathode surface, adjacent ones 
of the first members cooperating with the plate and the exposed cathode 
surface to form at least one air conducting channel. 
In operation, at least a portion of the heat generated exothermically in 
the membrane electrode assembly is dissipated to the atmosphere through 
the first members. 
The thermally conductive plate is preferably, but not necessarily, formed 
as a single planar piece from which the thermally conductive members 
extend. Alternatively, the plate could consist of a plurality of staggered 
bars interconnecting the thermally conductive members, which extend from 
the staggered bars and contact the exposed cathode surface. 
The plate and the first members are preferably formed of aluminum, and the 
portions of the first members which contact the cathode surface have an 
inert metal applied thereto. The inert metal is preferably gold applied by 
electroplating. 
The preferred electrical connection means comprises electrical conductors 
disposed between the anode and the ion exchange membrane, and the 
electrical conductors preferably extend through the sealing means. The 
preferred electrical conductors are formed from gold wire. 
In the preferred assembly, the plate has a thermally conductive material 
extending from another major surface of the plate, such that heat 
generated exothermically in the membrane electrode assembly is further 
dissipated to the atmosphere through the material. The material preferably 
comprises a plurality of thermally conductive members, or alternatively a 
thermally conductive foam. The preferred thermally conductive foam is an 
aluminum foam. 
In the preferred assembly, the fuel delivery means comprises a fuel inlet 
and a fuel outlet, such that the fuel outlet directs unreacted components 
of the gaseous fuel stream away from the anode. The assembly can further 
comprise a fan for directing the ambient air onto the exposed surface of 
the porous electrically conductive cathode. Where the gaseous fuel stream 
comprises hydrogen, the assembly preferably further comprising means for 
accumulating water condensed on the first thermally conductive members. 
A fuel cell stack incorporating the above fuel cell assemblies comprises: 
1. a plurality of fuel cell assemblies as defined with components (a)-(e) 
above; 
2. serial connection means for electrically connecting the plurality of 
fuel cell assemblies in an electrical series having a first assembly and a 
last assembly, wherein the anode of each assembly except the last assembly 
in the series is electrically connected to the cathode of the next 
adjacent assembly in the series; 
3. a positive current lead electrically connected to the cathode of the 
first assembly in the series; and 
4. a negative current lead electrically connected to the anode of the last 
assembly in the series. 
The fuel cell stack can be formed as a multiplexed arrangement, wherein the 
plurality of fuel cell assemblies share a common ion exchange membrane. 
The above and other objects are also achieved by an electrochemical fuel 
cell assembly comprising: 
(aa) a bicell membrane electrode assembly comprising a first porous 
electrically conductive cathode having a surface thereof exposed to 
ambient air, a porous electrically conductive anode, a second porous 
electrically conductive cathode having a surface thereof exposed to 
ambient air, a first ion exchange membrane interposed between the first 
cathode and the anode, and a second ion exchange membrane interposed 
between the second cathode and the anode; 
(bb) sealing means for forming a gas-impermeable barrier around the anode; 
(cc) fuel delivery means for delivering gaseous fuel to the anode; 
(dd) electrical connection means for providing an electrical connection to 
the anode, to the first cathode and to the second cathode; 
(ee) a first thermally conductive plate having a plurality of first 
thermally conductive members extending from a major surface of the plate, 
the first members contacting portions of the exposed first cathode 
surface, adjacent ones of the first members cooperating with the first 
plate and the exposed first cathode surface to form at least one air 
conducting channel; and 
(ff) a second thermally conductive plate having a plurality of second 
thermally conductive members extending from a major surface thereof, the 
second members contacting portions of the exposed second cathode surface, 
adjacent ones of the second members cooperating with the second plate and 
the exposed second cathode surface to form at least one air conducting 
channel. 
In operation, at least a portion of the heat generated exothermically in 
the bicell membrane electrode assembly is dissipated to the atmosphere 
through the first and second members. 
The first and second members are preferably formed of aluminum, the 
portions of the first and second members which contact the cathode 
surfaces have an inert metal applied thereto. The inert metal is 
preferably gold applied by electroplating. 
The electrical connection means preferably comprises first electrical 
conductors disposed between the anode and the first membrane, and second 
electrical conductors disposed between the anode and the second membrane, 
such that the first and second electrical conductors extending through the 
sealing means. The first and second electrical conductors are preferably 
formed from gold wire. 
In the preferred bicell assembly, the first plate has a first thermally 
conductive material extending from another major surface of the first 
plate, and the second plate has a second thermally conductive material 
extending from another major surface of the second plate, such that heat 
generated exothermically in the bicell membrane electrode assembly is 
further dissipated to the atmosphere through the first and second 
material. The first and second material each preferably comprises a 
plurality of thermally conductive members, or alternatively a thermally 
conductive foam. The preferred thermally conductive foam is an aluminum 
foam. 
In the preferred bicell assembly, the sealing means comprises the first and 
second membranes, such that the edges of the first and second membranes 
are bonded together to form a gas-impermeable barrier around the anode. 
In the preferred bicell assembly, the fuel delivery means comprises a fuel 
inlet and a fuel outlet, such that the fuel outlet directs unreacted 
components of the gaseous fuel stream away from the anode. The preferred 
bicell assembly further comprises a fan for directing the ambient air onto 
the exposed surface of the porous electrically conductive cathode. Where 
the gaseous fuel stream comprises hydrogen, the bicell assembly preferably 
further comprising means for accumulating water condensed on the first and 
second thermally conductive members. 
A bicell stack incorporating the above bicell assemblies comprises: 
I. a plurality of fuel cell assemblies as defined with components (aa)-(ff) 
above; 
II. serial connection means for electrically connecting the plurality of 
bicell assemblies in an electrical series having a first assembly and a 
last assembly, wherein the anode of each assembly except the last assembly 
in the series is electrically connected to the cathodes of the next 
adjacent assembly in the series; 
III. a positive current lead electrically connected to the cathodes of the 
first assembly in the series; and 
IV. a negative current lead electrically connected to the anode of the last 
assembly in the series. 
The bicell stack can be formed as a multiplexed arrangement, wherein the 
plurality of bicell assemblies share a common first ion exchange membrane 
and a common second ion exchange membrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1 and FIG. 2A, an electrochemical fuel cell 
assembly 10, includes a bicell membrane electrode assembly ("MEA") 14. 
Bicell MEA 14 includes a first cathode 16, an anode 26, and a second 
cathode 38. A first ion exchange membrane 24 is interposed between first 
cathode 16 and anode 26. A second ion exchange membrane 34 is interposed 
between second cathode 38 and anode 26. Fuel supply line 44 and fuel inlet 
46 contain and direct fuel at a pressure slightly greater than atmospheric 
to anode 26. 
The electrodes 16, 26, 38 are formed of porous electrically conductive 
sheet material, preferably porous carbon fiber paper ("CFP") impregnated 
or coated with a hydrophobic polymer, such as polytetrafluoroethylene. The 
electrodes 16, 26, 38 are each treated with a layer of catalyst, such as 
platinum or other suitable electrocatalytic material, on the surface(s) 
adjacent and in contact with the ion exchange membrane(s) 24, 34 to 
facilitate the desired chemical reaction. Suitable ion exchange membranes 
are commercially available from DuPont under the trade name Nafion 117 and 
from Dow under the trade designation XUS 13204.10. 
The electrodes 16, 26, 38 and the ion exchange membranes 24, 34 are 
arranged together in an interleaved or sandwich-like manner, as 
illustrated in FIG. 1 and FIG. 2A, and placed in a high pressure press at 
a temperature sufficient to soften the ion exchange membrane material. The 
combination of pressure and temperature forces the softened membrane 
material at least partially into the CFP electrode material, bonding the 
individual layers to form a single unitary assembly. Presently, the bicell 
MEA 14 is formed by placing the layers of material in a press at a 
temperature and pressure sufficient to soften the material and create an 
intimate bond. 
Low pressure can be employed to supply the gaseous fuel because the 
chemical reaction at the anode 26 consumes the fuel and draws it into the 
anode 26. The porous structure of the CFP used to form the anode 26 
facilitates the delivery of the gaseous fuel throughout the anode 26. The 
gaseous fuel reacts at the anode 26 to produce cations (protons) and 
electrons. When hydrogen is used as the fuel, the reaction at the anode 
produces hydrogen cations and electrons according to the following 
equation: 
EQU H.sub.2 .fwdarw.2H.sup.+ +2e.sup.-. 
The reaction at the cathodes 16, 38 produces water according to the 
following equation: 
EQU 1/2O.sub.2 +2H.sup.+ +2e.sup.- .fwdarw.H.sub.2 O. 
The ion exchange membrane facilitates the migration of cations from the 
anode 26 to the cathodes 16, 38. In addition to conducting hydrogen 
cations, the ion exchange membranes 24, 34 isolate the gaseous fuel stream 
from the oxidant stream. This is particularly important when hydrogen is 
employed as a fuel source because of the reaction which occurs when 
hydrogen and oxygen are mixed and ignited or contacted with a catalyst. 
A seal 50 provides a gas-impermeable barrier at the edges of the anode 26 
to prevent leakage of the gaseous fuel from Within anode 26. In FIG. 2A, 
the seal 50 is formed by extending the ion exchange membranes 24, 34 over 
the edges of the anode 26. During the assembly process, the portions of 
the ion exchange membranes 24, 34 extending over the anode 26 can be 
adhered using heat and pressure to form a gas-impermeable seal around the 
anode 26. Alternatively, as illustrated in FIB. 2B, the seal 50 may be 
formed by disposing layers of sealant 52a, 52b, such as a silicon based 
sealant, along the top and bottom edge portions, respectively, of anode 26 
which extend between the ion exchange membranes 24, 34. 
As shown in FIGS. 1, 2A and 2B, edge current collectors 56a, 56b are 
disposed between the anode 26 and the ion exchange membranes 24, 34. The 
first edge current collector 56a is disposed between the anode 26 and the 
first ion exchange membrane 24, and the second edge current collector 56b 
is disposed between the anode 26 and the second ion exchange membrane 34. 
The edge current collectors 56a, 56b facilitate current flow (i.e., 
electron flow) from the anode 26 to an external load, as described in more 
detail below. As best shown in FIG. 2A, the edge current collectors 56a, 
56b exit the bicell MEA 14 through the seal 50, thereby providing an 
electrical connection to the anode 26. 
Each of the edge current collectors 56a, 56b is preferably formed from a 
plurality of electrically conductive wires (not shown). The wires forming 
the edge current collectors 56a, 56b are in turn preferably formed from a 
highly conductive material such as gold, niobium, platinum, titanium or 
graphite. Although a single wire can provide sufficient edge current 
collection, a plurality of wires is preferred. In FIG. 1, the conductive 
wires 56a, 56b are shown exiting from both the top and bottom of the 
bicell MEA 14, whereas in FIGS. 2A and 2B the conductive wires only exit 
from the top of the bicell MEA 14. 
As shown in FIGS. 1, 2A and 2B, the fuel cell assembly 10 further includes 
first and second thermally conductive plates 62a, 62b disposed on opposite 
sides of the bicell MEA 14. The plates 62a, 62b are preferably constructed 
from aluminum which is either milled or extruded to form the illustrated 
configuration. Aluminum is preferred because it is relatively inexpensive 
and lightweight and because it has favorable thermal and electrical 
conductivity. 
As shown in FIG. 1, each plate 62a, 62b includes a first set of thermally 
conductive members, shown in FIG. 1 as fins 66a, 66b, which extend toward 
the bicell MEA 14 and contact one of cathodes (cathode 38 in FIG. 1 and 
FIG. 2A) and a second set of thermally conductive members, shown in FIG. 1 
as fins 64a, 64b, which extend away from the bicell MEA 14. The portion of 
each fin 66a, 66b which contacts the surface of a cathode is preferably 
plated with gold to prevent oxidization of the aluminum and ensure good 
electrical contact between the cathode 38 and each fin 66a, 66b. 
The first set of thermally conductive members 66a, 66b provide structural 
rigidity and support for the bicell MEA 14, stabilize the MEA 14, and 
inhibit distortion of the MEA 14 from swelling due to oversaturation of 
the membrane. 
Each of the second set of thermally conductive members, shown in FIG. 1 as 
fins 64a, 64b, could also be formed as a thermally conductive foam, in 
lieu of the fins. Thermally conductive foam has an irregular 
three-dimensional conformation, with interstitial spaces permitting the 
passage of air and other coolant fluids through the irregular, 
lattice-like structure of the thermally conductive material from which the 
foam if formed. The preferred thermally conductive foam is an aluminum 
foam. 
As shown in FIG. 1, a fastener mechanism secures the plates 62a, 62b and 
MEA 14 in assembled form and maintains contact between the fins 66a, 66b 
and the exposed surfaces of cathodes 16, 38. The fastener mechanism 
preferably includes a first threaded fastener 72 extending through the 
upper portion of the plates 62a, 62b and a second threaded fastener 74 
extending between the bottom portion of the plates 62a, 62b. The threaded 
fasteners 72, 74 connect the plates 62a, 62b and allow the plates 62a, 62b 
to be clamped against the bicell MEA 14, thereby maintaining electrical 
and physical contact between the cathodes 16, 38 and the plates 62a, 62b. 
Both sets of fins 64a, 64b and 66a, 66b are open at the top and bottom to 
allow air flow through the fins. Heat produced by the exothermic chemical 
reaction of fuel (hydrogen) and oxidant (oxygen) within the bicell MEA 14 
is dissipated to the atmosphere through the fins 64a, 64b and 66a, 66b. It 
has been found that such heat dissipation produces a natural convection 
current which causes the ambient air to be drawn upwardly through the fins 
64a, 64b and 66a, 66b. The set of fins 64a extend in a direction away from 
MEA 14, and function primarily as heat transfer surfaces for expelling 
waste heat to the atmosphere such that a desired operation temperature of 
the bicell MEA 14 is maintained. The sets of fins 66a, 66b, in addition to 
functioning as heat transfer surfaces, cooperate with the plates 62a, 62b 
and the adjacent cathodes to form a plurality of air conducting channels 
which draw oxygen-containing ambient air toward the exposed surface of the 
cathodes. For example, fins 66a cooperate with plate 62a and cathode 16 to 
form an air conducting channel 78 (see FIG. 1). A similar plurality of air 
conducting channels draws oxygen-containing ambient air toward the exposed 
surface of cathode 38. The vertical orientation of the air supply channels 
78 allows the water produced at the cathode 16 to flow downwardly toward 
the bottom of the fuel cell assembly 10 where it can be drained from the 
assembly, thereby preventing oversaturation of the ion exchange membrane 
24. 
In employing ambient air as the oxidant and coolant for the fuel cell 
assembly 10, the following operating conditions should be present: 
(1) ambient air flow through the air conducting channels to provide a 
sufficient stoichiometric supply of reactant oxygen to support the 
reaction at the membrane electrode assembly; 
(2) ambient air flow and operating temperature should be such that the 
water removal capacity of the ambient air flow is less than the rate of 
production of reactant water to prevent dehydration of the ion exchange 
membranes; 
(3) the operating temperature of the cell should be high enough to provide 
reasonable fuel cell performance; and 
(4) the operating temperature of the fuel cell should be high enough to 
allow the cell to reject waste heat to the atmosphere by natural 
convection. 
With these considerations in mind, the size, spacing, and number of members 
or fins is empirically optimized to provide temperature stability and 
performance stability over a wide range of loads. 
Turning now to FIG. 3, a plurality of the fuel cell assemblies, six of 
which are designated in FIG. 3 as assemblies 10a, 10b, 10c, 10d, 10e, and 
10f, can be combined to form a fuel cell stack 100. Fuel inlets, one of 
which is designated in FIG. 3 as fuel inlet 146, each direct a fuel stream 
to one of the respective fuel cell assemblies 10a-f. The fuel inlets are 
connected to a main fuel supply line 104, which is in turn connected to a 
fuel supply source (not shown) for delivering gaseous fuel at a pressure 
slightly greater than atmospheric to the stack 100. 
In FIG. 3, the fuel cells assemblies 10a-f are electrically connected in 
series so that the fuel cell stack 100 produces a voltage potential equal 
to the sum of the voltages of the individual fuel cell assemblies 10a-f. 
More specifically, the edge current collectors 156 are used to 
electrically couple the anode of one bicell MEA to the cathodes of the 
next adjacent bicell MEA in the stack 100. For example, in FIG. 3 the 
anode of the first fuel cell assembly 10a is electrically connected to the 
cathodes of the second fuel cell assembly 10b. This electrical connection 
is preferably made by connecting the edge current collectors 156 from one 
fuel cell assembly to the plate 162 adjacent the next fuel cell assembly 
in the stack 100. 
The full electrical potential of the stack 100 is imposed between a 
positive lead 108 and a negative lead 110. The positive lead 108 is formed 
by connecting an electrical conductor 112 to a positively charged portion 
of the first cell 10a in the stack 100. Specifically, the positive lead 
108 can be connected to either of the end plates, the fins, the threaded 
fasteners, or the cathodes of the first cell 10a. The negative lead 110 is 
formed by joining the edge current collectors of the last fuel cell 
assembly 10f to form a single conductor 114. 
As is illustrated schematically in FIB. 3, when the stack 100 is installed 
in an electrical circuit, a load 118 and a contactor switch 120 can be 
connected between the positive and negative leads 108, 110. The contactor 
switch 120 can be selectively opened and closed to deliver power from the 
stack 100 to the load 118. 
FIBS. 4A and 4B illustrate alternative embodiments for serially connecting 
individual bicell MEAs to form a stack configuration. In both FIGS. 4A and 
4B, the electrodes of successive bicell MEAs are interleaved to form 
serial electrical connections. Each bicell MEA 114 includes a center anode 
116 interposed between two cathodes 120, 122. Two sheets of solid polymer 
ion exchange membranes 126, 128 are interposed between the anode 116 and 
the cathodes 120, 122. In FIG. 4A, sealant material 132 is disposed at 
both ends of the anode 116 to prevent leakage of the gaseous fuel supplied 
to the anode 116. In FIG. 4B, a single sheet of material is used to form 
ion exchange membranes 126, 128. The membrane material is looped around 
one end of the anode 116 and sealant material 132 is used to seal the 
other end of the anode 116. 
In both embodiments illustrated in FIGS. 4A and 4B, the cathodes 120, 122 
extend beyond one end of a respective anode 116 and are joined around an 
electrical conductor 136. The electrical conductor 136 in turn extends 
through the sealant 132 and into the anode 116 of the next bicell MEA 114b 
in the stack. 
FIB. 5 illustrates an alternative embodiment of a fuel cell assembly which 
employs ambient air as the oxidant and coolant. In FIG. 5, a unicell MEA 
214 is employed as opposed to the bicell MEA arrangement of FIGS. 1, 2A 
and 2B. MEA 214 includes an ion exchange membrane 224, which is interposed 
between anode 226 and cathode 216. A seal 250, formed of sealant material 
disposed along the exterior surfaces of the anode 226, is also shown in 
FIG. 5. Seal 250 forms a gas-impermeable barrier to prevent leakage of 
gaseous fuel supplied to the anode 226. A fuel delivery mechanism 244 
delivers gaseous fuel (preferably substantially pure hydrogen) to the 
anode 226 of the unicell MEA 214. The fuel delivery means 244 includes at 
least one fuel inlet 246 which extends partially into the anode 226. The 
fuel inlet 246 delivers gaseous fuel to the anode 226 at a low pressure or 
at slightly greater than atmospheric pressure. 
In the embodiment illustrated in FIG. 5, a clamping mechanism 218 secures 
the plate 262, together with its fins 264, 266, against the cathode 216 of 
the unicell MEA 214. The clamping means 218 is illustrated in FIG. 5 as a 
pair of threaded fasteners 272, 274 and an end plate 220. 
FIG. 6 shows a multiplexed arrangement 302 of three bicell assemblies 
employing ambient air as the oxidant and coolant. The multiplexed 
arrangement includes first cathodes 304a, 304b, 304c, anodes 306a, 306b, 
306c, and second cathodes 314a, 314b, 314c. As shown in FIG. 6, first 
cathode 304a, anode 306a and second cathode 314a are arranged in a first 
bicell MEA 310a, with first ion exchange membrane 316 interposed between 
first anode 306a and cathode 304a, and second ion exchange membrane 326 
interposed between anode 306a and second cathode 314a. Similarly, first 
cathode 304b, anode 306b and second cathode 314b are arranged in a second 
bicell MEA 310b, with first ion exchange membrane 316 interposed between 
first anode 306b and cathode 304b, and second ion exchange membrane 326 
interposed between anode 306b and second cathode. 314b. Finally, first 
cathode 304c, anode 306c and second cathode 314c are arranged in a third 
bicell MEA 310c, with first ion exchange membrane 316 interposed between 
first anode 306c and cathode 304c, and second ion exchange membrane 326 
interposed between anode 306c and second cathode 314c. As shown in FIG. 6, 
first, second and third bicell assemblies 310a, 310b, 310c share a common 
first ion exchange membrane 316 and a common second ion exchange membrane 
326. FIG. 6 also shows the location of one of the thermally conductive 
member or fin subassemblies 360. Fin subassembly 360 includes a thermally 
conductive plate 362, a first set of thermally conductive members or fins 
366, which extend toward bicell MEA 310b and contact cathode 304b, and a 
second set of thermally conductive members or fins 364, which extend away 
from bicell MEA 310b. Channels 332a and 332b are the fuel flow channels 
which interconnect the anodes in the multiplexed arrangement 302 shown in 
FIG. 6. Multiplexed arrangement 302 is sealed on both ends by seals 320a, 
320b, preferably formed by the fusing together of first and second ion 
exchange membranes 316, 326. 
FIG. 7 shows a thermally conductive member or fin subassembly 460 which 
employs a slidable comb 462 for adjusting the configuration of the air 
conducting channels. The air conducting channels are formed by the spaces 
between the fins, one of which is designated in FIG. 7 as fin 466a. As 
shown in FIG. 7, slidable comb 462 includes a plurality of tines 462a, 
which extend into the channels formed by the spaces between the fins. 
FIG. 8 shows another fin subassembly 560 which employs pivotable baffles 
(one of which is shown in phantom lines in FIG. 8 as baffle 574a). Fin 
subassembly 560 includes a thermally conductive plate 562. A plurality of 
thermally conductive fins 566a, 566b, 566c, 566d extend from one major 
surface of plate 562. In the completed fuel cell assembly incorporating 
fin subassembly 560, fins 566a-d contact the outwardly facing surface of 
the adjacent cathode (not shown in FIG. 8). A plurality of thermally 
conductive fins 564a, 564b, 564c, 564d, 564e, 564f extend from the other 
major surface of plate 562. Each of fins 564a-f has a slotted opening 
formed therein, one of which is shown in FIG. 8 as slot 570. A pivotable 
baffle subassembly, one baffle of which is shown in FIG. 8 as baffle 574a, 
is suspended in the slots by pivot pin 572. Rotation of baffle 574a about 
pivot pin 572 regulates the amount of air flow through the air conducting 
channels. 
Arrows A in FIG. 8 show the direction of air flow through the channels 
formed between fins 566a-d, and represent the air supply for the 
electrochemical reaction at the adjacent cathode (not shown). Arrow B in 
FIG. 8 shows the direction of air flow through the channels formed between 
fins 564a-f, and represents the air supply for conducting heat from the 
adjacent fuel cell structure (not shown), thereby providing thermal 
management to the adjacent fuel cell structure. 
FIG. 9 shows pivotable baffle subassembly 574 for use in conjunction with 
the fin subassembly 560 in FIG. 8. Subassembly 574 includes a plurality of 
baffles 574a, 574b, 574c mounted on central pivot pin 572. FIG. 10 shows a 
side view of pivotable baffle subassembly 574. 
FIG. 11 shows schematically an electrochemical fuel cell assembly employing 
ambient air as the oxidant and coolant, which employs external dampers 
676, 678 having pivotable baffles 674, 684, respectively, for adjusting 
the flow through the air conducting channels 664, 666. In FIG. 11, anode 
626, ion exchange membrane 624 and cathode 616 form the membrane electrode 
assembly. Fins (not shown) extend from each major surface of plate 662. 
The spaces formed between the extending fins form air conducting channels 
664, 666. Dampers 676, 678 include baffles 674, 684, which are mounted on 
pivot pins 672, 682, respectively. Rotation of baffle 674, 684 about the 
respective pivot pins 672, 682 regulates the amount of air flow through 
the air conducting channels 664, 666. 
While particular elements, embodiments and applications of the present 
invention have been shown and described, it will be understood, of course, 
that the invention is not limited thereto since modifications may be made 
by those skilled in the art, particularly in light of the foregoing 
teachings. It is therefore contemplated by the appended claims to cover 
such modifications as incorporate those features which come within the 
spirit and scope of the invention.