Integrated main rail, feed rail, and current collector

A separator plate for a fuel cell comprising an anode current collector, a cathode current collector and a main plate, the main plate disposed between the anode current collector and the cathode current collector. The anode current collector forms a flattened peripheral wet seal structure and manifold wet seal structure on the anode side of the separator plate and the cathode current collector forms a flattened peripheral wet seal structure and manifold wet seal structure on the cathode side of the separator plate. In this manner, the number of components required to manufacture and assemble a fuel cell stack is reduced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to internally manifolded and internally manifolded 
and internally reformed fuel cell stacks, and in particular, subassemblies 
of an anode/current collector/separator plate/current collector/cathode 
therefor which upon assembly with electrolyte provide wet seals between 
the electrolyte and the electrodes. The subassemblies provide ease of 
assembly resulting in reduced labor costs and long term stability and the 
separator plate design reduces the amount of material required for 
fabrication, in particular, of the main and feed rails comprising the wet 
seals, resulting in reduced material costs. In accordance with one 
embodiment, the separator plate design provides integration of the current 
collector and main rail and elimination of a separate feed rail. 
This invention is particularly applicable to molten carbonates and solid 
conductor/solid oxide fuel cells. 
Generally, fuel cell electrical output units are comprised of a stacked 
plurality of individual cells separated by inert or hi-polar 
electronically conductive ferrous metal separator plates. Individual cells 
are sandwiched together and secured into a single stacked unit to achieve 
desired fuel cell energy output. Each individual cell generally includes 
an anode and cathode electrode, a common electrolyte "tile" or "matrix", 
typically referred to as the active area components, and a fuel and 
oxidant gas source. Both fuel and oxidant gases are introduced through 
manifolds to their respective reactant chambers between the separator 
plate and the electrolyte tile. The area of contact between the 
electrolyte and other cell components to maintain separation of the fuel 
and oxidant gases and prevent and/or minimize gas leakage is known as the 
wet seal. A major factor contributing to premature fuel cell failure is 
corrosion and fatigue in the wet seal area. This failure is hastened by 
thin-film electrolyte corrosion of stainless steel surfaces of the 
separator plate at high temperatures and high thermal stresses resulting 
from differing thermal expansion characteristics between the separator 
plate and active area components during thermal cycling of the cell, 
causing weakening of the electrolyte tile structure through 
intracrystalline and transcrystalline cracking. Such failures permit 
undesired fuel and/or oxidant gas crossover and overboard gas leakage 
which interrupts the intended electrochemical oxidation and reduction 
reactions, thereby causing breakdown and eventual stoppage of cell current 
generation. Under fuel cell operating conditions, in the range of about 
500.degree. C. to about 700.degree. C., molten carbonate electrolytes are 
very corrosive to ferrous metals which, due to their strength, are 
required for fuel cell housings and separator plates. The high temperature 
operation of stacks of molten carbonate fuel cells increases both the 
corrosion and thermal stress problems in the wet seal area, especially 
when the thermal coefficients of expansion of adjacent materials are 
different. 
This invention provides fully internal manifolding of the fuel and oxidant 
gases to and from the individual cells of an assembled stack in a manner, 
due to the design of the cell components, which provides ease of assembly, 
long term endurance, stability of fuel cell operation, and a reduced 
number of individual cell components, thereby eliminating fit up problems 
between the various cell components. 
2. Description of the Prior Art 
Commercially viable molten carbonate fuel cell stacks may contain up to 
about 600 individual cells, each having a planar area in the order of at 
least eight square feet. In stacking such individual cells, separator 
plates separate the individual cells with fuel and oxidant each being 
introduced between a set of separator plates, the fuel being introduced 
between one face of a separator plate and the anode side of an electrolyte 
matrix and oxidant being introduced between the other face of the 
separator plate and the cathode side of a second electrolyte matrix. Due 
to the thermal gradients between cell assembly and cell operating 
conditions, differential thermal expansions, and the necessary strength of 
materials used for the manifolds, close tolerances and very difficult 
engineering problems are presented. 
Conventionally, stacks of individual molten carbonate fuel cells have been 
constructed with spacer strips around the periphery of a separator plate 
to form wet seals. Various means of sealing in the environment of the high 
temperature fuel cell wet seal area are disclosed in U.S. Pat. No. 
4,579,788 which teaches wet seal strips fabricated utilizing powder 
metallurgy techniques; U.S. Pat. No. 3,723,186 which teaches the 
electrolyte itself comprised of inert materials in regions around its 
periphery to establish an inert peripheral seal between the electrolyte 
and frame or housing; U.S. Pat. No. 4,160,067 which teaches deposition of 
inert materials onto or impregnated into the fuel cell housing or 
separator in wet seal areas; U.S. Pat. No. 3,867,206 which teaches a wet 
seal between electrolyte-saturated matrix and electrolyte-saturated 
peripheral edge of the electrodes; U.S. Pat. No. 4,761,348 which teaches 
peripheral rails of gas impermeable material to provide a gas sealing 
function to isolate the anode and cathode from the oxidant and fuel gases, 
respectively; U.S. Pat. No. 4,329,403 which teaches a graded electrolyte 
composition for a more gradual transition in the coefficient of thermal 
expansions in passing from the electrodes to the inner electrolyte region; 
and U.S. Pat. No. 3,514,333 which teaches housing of alkali metal 
carbonate electrolytes in high temperature fuel cells by use of a thin 
aluminum sealing gasket. None of the above patents deal with sealing 
around internal fuel and oxidant manifolds in fuel cell stacks. 
U.S. Pat. No. 4,510,213 teaches transition frames surrounding the active 
portion of the cell units to provide fuel and oxidant manifolds to the gas 
compartments of the individual cells, the manifolds not passing through 
the separators nor the electrolyte tiles of the cells. The transition 
frames require complicated insulating between adjacent cells and are made 
up of several separate and complicated components. U.S. Pat. No. 4,708,916 
teaches internal manifolding of fuel and external manifolding of oxidant 
for molten carbonate fuel cells in which sets of fuel manifolds pass 
through electrodes as well as electrolytes and separators in a central 
portion and at opposite ends of the individual cells to provide shortened 
fuel flow paths. The end fuel manifolds are in a thickened edge wall area 
of the separator plate while the central fuel manifolds pass through a 
thickened central region and sealing tape impregnated with carbonate or 
separate cylindrical conduit inserts are provided extending through the 
cathode. 
Internal manifolding has been attempted wherein multiple manifold holes 
along opposite edges of the cell have been used to provide either co- or 
counter-current flow of fuel and oxidant gases. These manifold holes for 
fuel have been located in a broadened peripheral wet seal area along 
opposing edges, but the manifolds have been complicated structures 
exterior to the electrolyte or passing through at least one of the 
electrodes. However, adjacent manifold holes are used for fuel and oxidant 
which provides short paths across a short wet seal area and leakage of the 
gases as well as the necessarily broadened peripheral seal area 
undesirably reducing the cell active area, as shown, for example, in U.S. 
Pat. No. 4,769,298. Likewise, prior attempts to provide internal 
manifolding have used multiple manifolded holes along broadened peripheral 
wet seal areas on each of all four edges of the cell to provide crossflow, 
but again, short paths between adjacent fuel and oxidant manifolds 
required similar complicated structures and the holes caused leakage of 
the gases and further reduced the cell active area. 
A fully internally manifolded molten carbonate fuel cell stack is taught by 
U.S. Pat. No. 4,963,442, U.S. Pat. No. 5,045,413, and U.S. Pat. No. 
5,077,148. each of which teaches a separator plate for a molten carbonate 
fuel cell stack having a flattened peripheral wet seal structure extending 
to contact the electrolytes on each face of the separator plates 
completely around their periphery forming a separator plate/electrolyte 
wet seal under cell operating conditions, and having a plurality of 
aligned perforations surrounded by a flattened manifold wet seal structure 
extending to contact the electrolyte on each face of the separator plate, 
forming a separator plate/electrolyte wet seal under cell operating 
conditions. In accordance with the teachings of these patents, the 
separator plates are pressed metal plates in which the flattened 
peripheral wet seal structure and the extended manifold wet seal structure 
on one face of the separator plate is a pressed shaping of the separator 
plate and on the other face of the separator plate is a pressed sheet 
metal shape fastened to said other face of the separator plate. In 
addition, conduits through the manifold wet seal structures are provided 
between one set of manifolds and anode chambers on one face of the 
separator plates for fuel gas and between the other set of manifolds and 
the cathode chambers on the other face of the separator plates for 
oxidant. These conduits are formed by corrugated metal or holes through 
sheet metal structures secured to the separator plate. Thus, a separator 
plate for a fuel cell unit in accordance with the teachings of these 
patents comprises as many as nine (9) individual pieces welded together 
and a fuel cell unit in accordance with the teachings of these patents 
comprises at least five (5) pieces in addition to the separator plate, 
namely, cathode and anode current collectors, cathode and anode electrodes 
and an electrolyte. In addition, to accommodate the current collectors and 
electrodes within the center portion of the separator plate, the wet seal 
structures are in the form of steps such that the current collectors and 
electrodes, when disposed in the center portion of the separator plates, 
are flush with the top portion of the step which forms the wet seal 
between the separator plate and the electrolyte. Such fit up of pieces 
into pressed steps results in variable elevational discontinuities which 
are known to cause cracking of the electrolyte and result in gas crossflow 
through the electrolyte tiles. 
SUMMARY OF THE INVENTION 
Accordingly, it is one object of this invention to provide a fuel cell unit 
having a reduced number of individual components. 
It is another object of this invention to provide a separator plate 
comprising a reduced number of components for assembly. 
It is another object of this invention to provide a fuel cell stack in 
which each of the components comprising the stack assembly extends to the 
peripheral edge of said stack. 
It is another object of this invention to provide a fuel cell unit in which 
the amount of waste material generated in the assembly thereof is reduced. 
It is yet another object of this invention to provide a design for a fuel 
cell unit which eliminates fit up problems between individual components 
of the fuel cell, in particular, the current collector and main and feed 
rails, that is, the peripheral and manifold wet seal structures, of the 
separator plate. 
These and other objects are achieved in a fuel cell stack in accordance 
with one embodiment of this invention comprising a plurality of fuel cell 
units, each of which fuel cell units comprises an anode and a cathode, an 
electrolyte in contact with one face of the anode and with an opposite 
facing face of the cathode and a separator plate separating each cell unit 
between the anode and cathode forming an anode chamber between one face of 
the separator plate and the anode and a cathode chamber between the 
opposite face of the separator plate and the cathode. The anode chamber is 
in gas communication with a fuel gas supply and outlet and the cathode 
chamber is in gas communication with an oxidant gas supply and outlet. The 
electrolytes and separator plates extend to the peripheral edge of the 
fuel cell stack, the separator plates having a flattened peripheral wet 
seal structure extending to contact the electrolytes on each face of the 
separator plates completely around their periphery forming a peripheral 
separator plate/electrolyte wet seal under cell operating conditions. The 
electrolytes and the separator plates each are provided with a plurality 
of aligned perforations, the perforations in the separator plates being 
surrounded by a manifold wet seal structure extending to contact the 
electrolyte on each face of the separator plate to form a manifold 
separator plate/electrolyte wet seal under cell operating conditions. The 
separator plate comprises an anode current collector, a cathode current 
collector and a main plate disposed between the anode current collector 
and the cathode current collector. The anode current collector forms the 
flattened peripheral wet seal structure and manifold wet seal structure on 
the anode side of the separator plate and the cathode current collector 
forms the flattened peripheral wet seal structure and manifold wet seal 
structure on the cathode side of the separator plate. Each of the current 
collectors is fastened to the main plate to provide peripheral seals 
between the current collectors and the main plate as well as peripheral 
manifold seals. The separator plate further comprises means for providing 
fuel gas communication between one set of the manifolds and the anode 
chambers on one face of each of the separator plates and means for 
providing oxidant gas communication between the other set of manifolds and 
the cathode chambers on the other face of each of the separator plates, 
thereby providing fully internal manifolding of fuel and oxidant gases to 
and from each said fuel cell unit in the fuel cell stack. 
In accordance with another embodiment of this invention, the separator 
plate comprises either an anode or cathode current collector and a main 
plate where the current collector forms the flattened peripheral wet seal 
structure and the manifolded wet seal structures on one face of the 
separator plate and the main plate forms the flattened peripheral wet seal 
structure and manifold wet seal structures on the other face of the 
separator plate. Thus, if the separator plate comprises an anode current 
collector, then the flattened peripheral wet seal structure and manifold 
wet seal structures formed by the main plate face the cathode and cathode 
current collector of the fuel cell unit. Likewise, if the separator plate 
comprises a cathode current collector, then the flattened peripheral wet 
seal structure and the manifold wet seal structures formed by the main 
plate face the anode and anode current collector. In accordance with this 
embodiment of the invention, the number of full-sheet sheet metal 
components required to manufacture a separator plate is reduced to two 
(2). To prevent gas leakage through passages formed between the main rails 
on both faces of the separator plate at least two (2) blocker-filler 
inserts in the form of a caulking to fill down-depressions pressed into 
the current collector/main rail are provided. 
In accordance with one embodiment of this invention, the current collectors 
are pressed metal plates comprising a plurality of openings in a central 
region and said aligned perforations, both of which are surrounded by a 
solid metal region. To form the flattened peripheral wet seal structure 
and the manifold wet seal structures in each of the current collectors, 
the metal plates are pressed, the solid metal regions surrounding the 
plurality of openings in the central region and the aligned perforations 
forming the flattened peripheral wet seal structure, or main rail, and the 
manifold wet seal structures, that is, also a main rail, or a feed rail. 
In accordance with a particularly preferred embodiment of this invention, 
the anode current collector and the anode are integrated with one another, 
forming a one piece anode/anode current collector. Similarly, the cathode 
and the cathode current collector are integrated with one another to form 
a one piece cathode/cathode current collector. 
In accordance with another embodiment of this invention, corrugations are 
provided in the region of the manifold wet seal structures through which 
oxidant gas flows from one set of manifolds to the cathode chambers on one 
face of the separator plates and fuel gas flows from a second set of 
manifolds to the anode chambers on the other face of the separator plates.

DESCRIPTION OF PREFERRED EMBODIMENTS 
A separator plate 10 for a molten carbonate fuel cell in accordance with 
one embodiment of this invention is shown in FIG. 1. Separator plate 10 
comprises main plate 11, cathode current collector 12, and anode current 
collector 13. Each of cathode current collector 12 and anode current 
collector 13 form peripheral cathode main rail 14 and peripheral anode 
main rail 15, respectively, which form peripheral wet seal structure 22 
shown in FIG. 2. Anode current collector 13 and cathode current collector 
12 are pressed metal plates comprising a plurality of openings 16 in a 
central region as shown in FIG. 1 and a plurality of perforations 23, 24 
as shown in FIG. 2. Both of said plurality of openings 16 and said 
perforations 23, 24 are surrounded by a solid metal region which form 
peripheral wet seal structure 22 comprising peripheral main rails 14, 15 
and manifold wet seal structure 25 as shown in FIG. 3 comprising blocker 
rail 19 or feed rail 20 depending upon the function of the corresponding 
manifold formed by perforations 23, 24, which wet seal structures are 
integral with anode current collector 13 and cathode current collector 12. 
That is, if it is intended that a fuel gas or oxidant flow between 
perforation 24 and anode chamber 17 or cathode chamber 18, then manifold 
wet seal structure 25 comprises feed rail 20. Where no such fuel gas or 
oxidant flow is desired, as for example between perforation 23 and cathode 
chamber 18, then manifold wet seal structure 25 comprises blocker rail 19. 
As shown in FIG. 6, perforation 23 aligns with corresponding perforations 
in anode current collector 30, anode electrode 31, bubble barrier 33, 
electrolyte 34, carbonate 35, and cathode electrode 36 to form anode feed 
manifold 29 through which fuel gas is provided to anode chamber 17 formed 
by main plate 11 and anode current collector 30. To provide gas 
communication between anode feed manifold 29 and anode chamber 17, a 
portion of manifold wet seal structure 25 comprises feed rail 20 forming 
feed rail openings 27 through which fuel gas flows from anode feed 
manifold 29 into anode chamber 17. 
In a particularly preferred embodiment of this invention, anode current 
collector 13, 30 is effectively eliminated by integration into the anode 
electrode to form an anode electrode/current collector and the anode main 
rail and feed rail functions are provided by the integrated anode 
electrode/current collector. Similarly, cathode current collector 12 is 
effectively eliminated by integration into the cathode electrode to form a 
cathode electrode/current collector and the cathode main rail and feed 
rail functions are provided by the integrated anode electrode/current 
collector. The result of this integration is a substantial reduction in 
the number of components comprising a fuel cell stack, thereby reducing 
the cost of assembly. 
Anode current collector 13, cathode current collector 12, and main plate 11 
extend to the peripheral edge of the fuel cell stack. To prevent leakage 
between components comprising separator plate 10, the peripheral edge of 
separator plate 10 is welded forming a seal 21 between the peripheral 
edges of cathode current collector 12, anode current collector 13, and 
main plate 11. The peripheral region of perforations 23, 24 are similarly 
welded to form seal 21a along the periphery of perforations of 23, 24 
between cathode current collector 12, anode current collector 13, and main 
plate 11. Thus, fluid flowing through anode feed manifold 29 and cathode 
manifold 37 are prevented from leaking between the components comprising 
separator plate 10. 
FIGS. 3, 4, and 5 show a particularly preferred embodiment of this 
invention in which separator plate 10 comprises cathode current collector 
12 with integrated cathode flattened peripheral wet seal structure 22a and 
main plate 11 with integrated anode flattened peripheral wet seal 
structure 22b. Separator plate 10 further comprises cathode current 
collector 12 with integrated cathode manifold wet seal structure 25a 
comprising blocker rail 19 and main plate 11 with integrated anode 
manifold wet seal structure 25b and feed rail 20. It will be apparent to 
those skilled in the art that anode current collector 13 may be 
substituted for cathode current collector 12 in which case the wet seal 
structures formed by main plate 11 are cathode wet seal structures. Thus, 
in accordance with this embodiment of the invention, it is apparent that a 
suitable separator plate for a fuel cell stack can be constructed of two 
pieces. 
FIG. 8 shows a portion of a 2-piece separator plate in accordance with one 
embodiment of this invention comprising main plate 11 and cathode current 
collector 12 with integrated cathode feed rail 51a. Conduits for oxidant 
flow into cathode chamber 18 as shown by arrow 71 are provided by slits 
70. To provide support for cathode current collector 12, a plurality of 
beams 72 are interspersed along the length of integrated cathode feed rail 
51a disposed between cathode current collector 12 and main plate 11 within 
the channel formed by integrated cathode feed rail 51a and integrated 
anode manifolded wet seal structure 51b. It will be apparent to those 
skilled in the art that a 2-piece separator plate in accordance with this 
embodiment of this invention may be formed using an anode current 
collector in place of cathode current collector 12. In accordance with 
such embodiment, main plate 11 forms an integrated cathode manifold wet 
seal structure. 
As shown in FIG. 7, the ends of feed rail 20 in accordance with one 
embodiment of this invention integrate with peripheral main rail 22 
providing possible communication between the channel formed between feed 
rail 20 on one face of the separator plate and the manifold wet seal 
structure on the opposite face of the separator plate. To close off such 
communication and thus prevent gas flow from feed rail 20 into peripheral 
main rail 22, impressions 50 are formed in the ends of the manifold wet 
seal structures which bottom out in feed rail 20 so as to effectively seal 
between the channel formed by feed rail 20 on one face of the separator 
plate and the manifold wet seal structure on the opposite face of the 
separator plate. The impression in the manifold wet seal structure is 
filled with a caulking material to provide continuity of the manifold wet 
seal formed under cell operating conditions. 
In accordance with another embodiment of this invention, as shown in FIG. 
9, the conduits for providing gas communication between anode feed 
manifold 29 and anode chamber 17 and cathode feed manifold 37 and cathode 
chamber 18 are in the form of corrugations 60 formed by feed rail 20. 
As previously stated, and as shown in FIG. 6, each of the components 
comprising separator plate 10 extends to the peripheral edge of the cell 
assembly. In addition, each of the remaining components of the cell 
assembly, namely, anode electrode 31, bubble barrier 33, electrolyte 34, 
carbonate 35, and cathode electrode 36, extend to the peripheral edge of 
the cell assembly. To protect the edges of cathode 36 which are exposed to 
hydrogen and to the anode feed and spent gas manifold, all such edges are 
protected with protective coating 32, such as aluminum. Similar protection 
is required for the edges of anode current collector 30, anode electrode 
31 and bubble barrier 33 which are exposed to air in the cathode feed and 
spent gas manifolds. Similarly, protection for anode electrode 31 and 
bubble barrier 33 is provided in the form of protective coating 32, 
protective coating 32 comprising aluminum foil or other suitable material. 
FIG. 1 shows peripheral cathode main rail 14 and peripheral anode main rail 
15 as steps, the remaining components of the cell assembly such as 
electrolyte tile 34, anode electrode 31 and cathode electrode 36 disposed 
within the recess adjacent the face of cathode current collector 12 and 
anode current collector 13 as appropriate. In a particularly preferred 
embodiment, particularly in view of the extension of all of the components 
of the cell assembly to the peripheral edge of the cell assembly, said 
step may be eliminated. 
While in the foregoing specification this invention has been described in 
relation to certain preferred embodiments thereof, and many details have 
been set forth for purpose of illustration, it will be apparent to those 
skilled in the art that the invention is susceptible to additional 
embodiments and that certain of the details described herein can be varied 
considerably without departing from the basic principles of the invention.