Solid electrolyte fuel cell

A planar solid electrolyte fuel cell includes a plurality of separators and electric insulators superposed one on another alternately in respective manifold parts of the separators. Each of the separators has a manifold part in the center thereof which are provided with two gas introduction holes and a reaction part provided with guide vanes surrounding the manifold part and for flowing reaction gases. Unit cells on porous substrates are each in the form of an annular plate with a single central hole. The separators sandwich the unit cells in the respective reaction parts thereof. Gas seal parts are provided around gas introduction holes, and gas seal parts are provided between the reaction parts of the separators and inner peripheral parts of the unit cells.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a solid electrolyte fuel cell and more 
particularly to a solid electrolyte fuel cell having a stack construction 
with improved thermal reliability. 
2. Description of the Prior Art 
Fuel cells using oxide solid electrolyte such as zirconia, which operate at 
high temperatures such as 800.degree. to 1,100.degree. C., not only 
exhibit high power generation efficiencies but also need no catalyst. Such 
fuel cells are easy to handle since the electrolytes used are solid. For 
this reason, it is expected that they will be employed as third generation 
fuel cells. 
However, the conventional solid electrolyte fuel cells are difficult to 
realize since they are susceptible to thermal damage because of the use of 
ceramics as their main construction components and the lack of a suitable 
method for providing seals for gases. Fuel cells having special forms, 
e.g., a cylindrical form, have been designed to solve the above-described 
problems have been and run successfully. However, the cylindrical fuel 
cells gave low power generation densities per volume of unit cell, and 
there has been no indication that they can provide economically 
advantageous fuel cells. 
FIG. 1 is an exploded perspective view showing a conventional planar or 
plate-like solid electrolyte fuel cell. As is well known, it is necessary 
to make fuel cells planar in order to increase power generation density. A 
fuel cell of this type includes a unit cell 17, and a separator plate 18. 
The unit cell 17 includes a solid electrolyte plate 17A which is of 
ceramics and electrodes 17B and 17C. Two separator plates 18,18 of 
ceramics and one unit cell 17 are alternately superposed one on another. 
In other words, the unit cell 17 is sandwiched by the two separator plates 
18, 18. The separator plates are each formed with first grooves and second 
grooves on different surfaces, running at right angles to each other, 
through which grooves different reaction gases flow, respectively. The 
reaction gases are introduced respectively thorough gas manifolds (not 
shown) into the fuel cell. 
For, example, in order to feed the reaction gases sufficiently and 
separately into the fuel cell, it becomes necessary to prevent leakage of 
gases between the unit cell 17 and the separator plate 18 around the 
periphery of the unit cell. To this end, it would seem to be a possible 
solution to render the unit cell 17 and the separator plate 18 integral by 
sintering them together. However, this method would be unsuccessful since 
the unit cell and the separator plate are-made of different materials and 
thermal stress could appear which would lead to cracks in the sintered 
body if there is even a slight difference in coefficient of thermal 
expansion or nonuniform temperature distribution between the materials. 
Accordingly, is has been contemplated to prevent leakage of gases using 
sealing materials. 
Japanese Patent Application Laying-open No. 267869/1990 discloses a solid 
electrolyte fuel cell which comprises a unit cell having a solid 
electrolyte on whose main surface are arranged an anode and a cathode, and 
first and second substrates sandwiching the unit cell and feeding reaction 
gases thereto, the resulting structure being superposed via an 
interconnector, in which (1) the first and second substrates have guide 
vanes arranged thereon that guide the reaction gases from the central 
parts toward the peripheral parts of the main surfaces, (2) the fuel cell 
includes reaction gas inlet pipes penetrating a stack composed of the 
first and second substrates, the unit cell, and the interconnector, in the 
central part thereof in the direction of the stack, the pipes being formed 
with gas ports on side surfaces thereof and for diffusing the gases toward 
the guide vanes, and (3) a glass seal is provided in spaces between the 
reaction gas inlet pipes and the inner periphery of the unit cell. 
Japanese Patent Application Laying-open No. 168568/1990 discloses a solid 
electrolyte fuel cell having a construction similar construction to that 
described in the above-cited publication in which a glass seal is provided 
in spaces between the first and second substrates and between the reaction 
gas inlet pipes as reaction gas feeding means. Optimally, a glass seal may 
be provided in spaces between the outer peripheral surface of the unit 
cell, and spaces between the outer peripheral surface and the reaction gas 
feeding means. 
Japanese Patent Application Laying-open No. 75262/1992 discloses a solid 
electrolyte fuel cell which comprises a plurality of first ribbed porous 
substrates each having on one surface thereof a unit cell, a plurality of 
second ribbed porous substrates each having on one surface thereof an 
interconnector, the first and second ribbed substrates being superposed 
one on another alternately, and first and second manifolds for feeding 
fuel gas and oxidant gas, respectively. The fuel cell further comprises a 
gas impermeable layer and a gas seal part. The unit cell is composed of 
three layers, i.e., an anode, a solid electrolyte and a cathode. Each 
first ribbed porous substrate has ribs which guide the fuel gas from the 
first manifold toward the peripheral part thereof on a surface opposite to 
the surface on which the unit cell is superposed. On the other hand, the 
second ribbed porous substrate has ribs which guide the oxidant gas from 
the second manifold toward the peripheral part thereof on a surface 
opposite to the surface on which the interconnector is superposed. The gas 
seal part is composed of a silver O-ring which is provided around the 
oxidant gas feeding manifold in the first ribbed porous substrate, and 
around the fuel gas feeding manifold in the second ribbed porous 
substrate. The gas impermeable layer is an O-ring made of glass or 
ceramics and intervenes between the gas seal parts and the ribbed porous 
substrates. Gas seal parts may be provided around the oxidant gas feeding 
manifold part in the anode and around the fuel gas feeding manifold part 
in the cathode, on the outer peripheral part of the first ribbed porous 
substrate, etc., as necessary. 
The use of the seal materials requires further improvement in the stability 
of the gas seal since both unit cells and separators are made of ceramics. 
SUMMARY OF THE INVENTION 
Under the circumstances, the present invention has been made. 
Therefore, an object of the present invention is to provide a solid 
electrolyte fuel cell which is highly reliable by adopting a cell 
construction having a stabilized gas sealing property without causing 
thermal destruction of the ceramics. 
The present invention provides a planar solid electrolyte fuel cell 
comprising: (1) a plurality of separator plates made of a metal, each 
having: a manifold part and a reaction part surrounding the manifold part, 
the manifold part being provided with two reaction gas introduction holes, 
and the reaction part being provided with first guide vanes on one surface 
thereof and second guide vanes on another surface thereof for flowing and 
distributing reaction gases therein separately; (2) a plurality of unit 
cells, each being in the form of an annular plate, and having an anode, a 
solid electrolyte and a cathode superposed one on another, each of the 
unit cells being sandwiched by two of the separators; (3) a plurality of 
electric insulators arranged on the central part of the separators, 
respectively, and being provided with two through holes aligned with the 
reaction gas introduction holes extending in a the direction of the 
thickness of the separators, the electric insulators and the separators 
being superposed one on another through the manifold parts of the 
separators, respectively; (4) first gas seal parts arranged between the 
manifold parts of the separators and the electric insulators, 
respectively, and for sealing off the reaction gases from the respective 
reaction gas introduction holes; and (5) second gas seal parts arranged 
between respective peripheral portions of the unit cells and the 
respective reaction parts of the separators sandwiching the unit cells. 
Here, the first and second gas seal parts may each be made of a mixture of 
glass and ceramic material. 
The separators may be made of a heat resistant metal. 
The separators may be made of a heat resistant stainless steel. 
The respective cathode sides of the separators may be provided with an 
antioxidant layer. 
The antioxidant layer may be made of LaXO.sub.3 wherein X is Mn, Cr or Co. 
The unit cells may be in the form of an annular plate formed with a single 
hole. 
The unit cells may each be a set of sectors. 
The solid electrolyte fuel cell may further comprise gas flow holes through 
which the reaction gas introduction holes in the manifold parts 
communicate with the reaction parts of the separators. 
The solid electrolyte fuel cell may further comprise gas flow holes and gas 
uniform distribution chambers, the gas flow holes communicating the gas 
uniform distribution chambers with the reaction gas introduction holes in 
the manifold parts of the separators. 
The unit cell may be a unit cell assembly having a porous substrate serving 
as one of the anode and the cathode, and the solid electrolyte and the 
rest of the anode and cathode are superposed on the porous substrate one 
on another in this order. 
According to the present invention, the reaction gases flow radially with 
respect to an annular, planar or flat plate-like unit cell, which makes 
distribution of temperature in the unit cell point-symmetrical, thus 
decreasing thermal destruction of the ceramics used. 
Moreover, according to the present invention, stability of the sealing 
property increases since the gas seal parts are formed via separators made 
of a metal. 
The above and other objects, effects, features and advantages of the 
present invention will become more apparent from the following description 
of embodiments thereof taken in conjunction with the accompanying drawings 
.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Hereinafter, the present invention will be described in more detail with 
reference to the attached drawings. 
Embodiment 1 
FIG. 2 is an exploded perspective view showing a solid electrolyte fuel 
cell according a first embodiment of the present invention; FIG. 3 is a 
cross sectional view taken along line 3--3 in FIG. 4 showing the solid 
electrolyte fuel cell according to the first embodiment of the present 
invention; and FIG. 4 is a cross sectional view taken along line 4--4 in 
FIG. 3 showing the solid electrolyte fuel cell according to the first 
embodiment of the present invention. 
As shown in FIGS. 2 to 4, separators 11 have a manifold part or region 40 
and a reaction part or region 42 surrounding the manifold part 40 
superposed one on another via electric insulator plates 21 provided in the 
manifold part. The separators 11 sandwich a unit cell assembly 33 in the 
reaction part 42. 
A first gas seal portion 6A prevents leakage of gases from gas introduction 
holes 4 and 5, respectively. A second gas seal portion 6B is formed 
between the reaction region of the separator 11 and an inner peripheral 
part 12A of a unit cell 12 and prevents leakage of gases between the 
reaction parts 42 of the separators 11 adjacent one another. 
In the central parts 40 of the separators serving as manifold parts, there 
are formed the gas introduction holes 4 and 5 for introducing therethrough 
fuel gas and oxidant gas, respectively. The manifold parts 40 of the 
separators 11 have protrusions 44. The protrusions 44 are formed with 
grooves 46 for inserting therein the gas seal portion 6A. The reaction 
part or region 42 of each separator 11 surrounding the manifold part 
thereof is provided with first and second sets of guide vanes 19A and 19B 
arranged on both surfaces thereof. The manifold part 40 of each separator 
11 is formed with gas flow holes 10A and 10B, as by drilling, which 
communicate with the gas introduction holes 4 and 5, respectively, and 
lead fuel and oxidant gases to the guide vanes 19B and 19A, respectively. 
The electric insulator 21, which is a dense disk made of ceramic, is 
provided with two through holes that match or are aligned with the gas 
introduction holes 4 and 5, respectively, to make a continuous gas conduit 
for supplying reaction gases, when the electric insulator 21 is superposed 
on the separator. 
Unit cells 12, which are each an annular disk formed with an inner hole 48, 
each include an anode 1, a solid electrolyte 3, and a cathode 2 that are 
superposed or laminated in this order on a porous substrate 7 having the 
Same form as the unit cell. Two separators 11 sandwich a unit cell 12 so 
that the protrusions 44 of the separators 11 and the electric insulator 21 
superposed thereon are arranged in the inner hole 48 of the unit cell with 
a suitable allowance between an inner peripheral surface 44A of the 
protrusion 44 and the electric insulator 21, and an inner peripheral 
surface 12A of the unit cell 12. One of the unit cells 12 and the 
respective reaction parts 42 of two of the separators 11 that sandwich the 
unit cell 12 therebetween define a fuel gas chamber 8 and an oxidant gas 
chamber 9 on opposite sides of the unit cell 12. In FIG. 3, the oxidant 
gas chamber is formed on the side of the cathode 2 while the fuel gas 
chamber 8 is formed on the side of the anode 1. 
Fuel cells of the aforementioned type can be fabricated as follows. First, 
there is formed a porous substrate 7 of 2 mm thickness using Ni--ZrO.sub.2 
(nickel-zirconia) cermet. Then, Ni--ZrO.sub.2 cermet is plasma-sprayed on 
a flat surface of the porous substrate to form a porous anode 1 of 50 
.mu.m thickness. Further, yttria-stabilized zirconia is plasma-sprayed on 
the anode 1 to form a dense solid electrolyte 3 of 100 .mu.m thick. 
Subsequently, lanthanum-strontium-manganite (La(Sr)MnO.sub.3) is 
plasma-sprayed on the solid electrolyte 3 to form a porous cathode 2 of 50 
.mu.m thickness. Then, a central part thereof is removed by processing to 
form a hole to obtain a unit cell 12 in the form of an annular disk. Glass 
is impregnated on the inner and outer peripheral surfaces of the porous 
substrate 7 to provide a gas impermeable layer 20. 
On the other hand, a separator 11 of 7 mm thickness is formed of stainless 
steel on both surface of which there are formed guide vanes 19A and 19B. 
Then, gas communication holes 10A and 10B communicating the gas 
introduction holes 4 and 5 with the guide vanes 19A and 19B are formed by 
discharge processing. 
The gas seal parts 6A and 6B are made of a mixture of glass and ceramic. 
The gas seal parts 6A and 6B can provide a liquid seal since the glass 
component therein becomes liquid at about 1000.degree. C. at which solid 
electrolyte fuel cells are operated. 
Oxygen gas, which is an oxidant gas, is led from the oxidant gas 
introduction hole 5 to the oxidant gas chamber 9 in the reaction part of 
the separator 11 through the gas flow hole 10B. Hydrogen gas, which is a 
fuel gas, is led through the fuel gas introduction hole 4 to the fuel gas 
chamber 8 in the reaction part of the separator 11 via the gas flow hole 
10A. The oxidant gas is exhausted from gas exhaust ports 16 arranged 
concentrically every 90.degree. (FIG. 4). Gas outlet ports for the fuel 
gas, defined between the guide vanes 19B which are concentrically 
arranged, distribute concentrically every 180.degree. rather than 
90.degree. since the flow rate of the fuel gas is low. 
The oxidant gas and fuel gas exhausted from the reaction part keep the 
temperature of the fuel cell within a predetermined temperature range. The 
gases are utilized as heat sources for preheating the reaction gases. 
The oxygen gas arriving at the cathode 2 is reduced to oxygen ions, which 
diffuse through the solid electrolyte 3 to the surface of the anode 1 
where they are oxidized and react with hydrogen gas to form water vapor. A 
free energy change in the reaction of forming water vapor from hydrogen 
gas and oxygen gas is converted into electric energy, with a negative 
voltage being generated on the anode 1 and a positive voltage on the 
cathode 2. The voltage per unit cell is 0.5 to 0.9 V, and a predetermined 
voltage can be obtained by piling up unit cells. 
In the case of the fuel cell having the aforementioned construction, it is 
only necessary that the porous substrate 7 on which the anode 1, the solid 
electrolyte 3 and the cathode 2 are formed and the separator 11 be 
superposed or piled up one on another alternately in order to obtain a 
fuel cell. This allows the porous substrates 7 and the separators 11 to 
move freely and independently of each other during thermal expansion, with 
the result that no thermal stress occurs. The gas seal part 6A arranged 
around the fuel gas introduction hole 4 and the gas seal part B arranged 
between the inner peripheral part of the unit cell 12 and separator 11 are 
solidified after operation of the fuel cell is stopped. However, this does 
not raise problem. Glass has a coefficient of thermal expansion greater 
than zirconia and other electrode materials and hence the gas seal parts 
after the solidification occupy smaller volumes, thus avoiding damages 
such as cracks to the other electrode materials. Since the thermal 
stresses given by the gas seal parts are small, the total thermal stress 
remains small. The gas seal parts 6A and 6B are made of a mixture of glass 
and a ceramic material and are filled in respective seal grooves (not 
shown) formed with the separator 11 which is made of a metal. This 
construction gives rise to a highly stable sealing performance. 
The contour of unit cells is usually an annular disk. However, it is not 
limited thereto but may be rectangular, ellipsoidal polygonal. The contour 
of the guide vanes of the separator may be designed freely taking into 
consideration uniform gas distribution. 
Embodiment 2 
FIG. 5 is a cross sectional view showing an example of the arrangement of a 
solid electrolyte according to a second embodiment of the present 
invention. 
In this embodiment, the separator and gas seal parts have the same 
structures as in Embodiment 1 but the unit cell structure and the 
composition of the porous substrate differ from those of the fuel cell 
described in Embodiment 1 above. 
On a porous substrate 13 which serves as a cathode 2 there are superposed a 
solid electrolyte 3 and an anode 1 to form a unit cell assembly 34. A unit 
cell 22 and the separator 11 are superposed one on another alternately. As 
described above, the manifold part of each separator 11 is provided with a 
fuel gas introduction hole 4 and an oxidant gas introduction hole 5. In 
this embodiment, however, the arrangement of reaction gas chambers are 
reversed. That is, a fuel gas chamber 8 is defined by the anode 1 and the 
guide vanes 19B while an oxidant gas chamber 9 is defined by the cathode 2 
and the guide vanes 19A unlike the fuel cell of Embodiment 1. 
A fuel cell of this type can be fabricated as follows. First, a porous 
substrate 13 of 2 mm thickness is formed using 
lanthanum-strontium-manganite (La(Sr)MnO.sub.3). On a flat surface of the 
porous substrate 13 thus formed there is plasma-sprayed La(Sr)MnO.sub.3 to 
form a porous cathode 2 of 80 .mu.m thickness. Then, yttria-stabilized 
zirconia is plasma-sprayed onto the cathode 2 to form a dense solid 
electrolyte 3 of 100 .mu.m thickness. Subsequently, nickel-zirconia cermet 
is plasma-sprayed on the solid electrolyte 3 to form a porous anode 1 of 
100 m thickness. Finally, a central part of the structure thus obtained is 
removed by processing to obtain a unit cell assembly 34 in the form of an 
annular flat plate. 
Embodiment 3 
FIG. 6 is a cross sectional view showing an example of the arrangement of a 
solid electrolyte according to a third embodiment of the present 
invention. 
The solid electrolyte fuel cell of this embodiment is similar to those 
described in Embodiments 1 and 2 except that it does not include a porous 
substrate unlike the preceding two embodiments. 
A unit-cell 32 is constituted by an anode 1, a solid electrolyte 3 and a 
cathode 2. The unit, cell 32 and a separator 11 are superposed one on 
another alternately. 
A solid electrolyte fuel cell of this type can be fabricated as follows. 
First, a dense sintered plate of yttria-stabilized zirconia (YSZ) of 0.5 
mm thickness is processed to have a hole in a central part thereof to make 
an annular plate. Then, a slurry of nickel-zirconia (Ni--ZrO.sub.2) cermet 
is coated on one surface of the annular plate, followed by sintering to 
form a porous anode 1 of 50 .mu.m thickness. On another surface of the 
annular plate there is coated a slurry of lanthanum strontium manganite 
(La(Sr)MnO.sub.3), which is then sintered to form a porous cathode 2 of 80 
.mu.m thickness. Thus a unit cell 32 is obtained. 
Embodiment 4 
FIG. 7 is a cross sectional view taken along line 7--7 in FIG. 8 showing an 
example of the arrangement of a solid electrolyte fuel cell according to a 
fourth embodiment of the present invention. FIG. 8 is a cross sectional 
view taken along line 8--8 in FIG. 7. 
An oxidant gas is introduced through an oxidant gas introduction hole 5 
into a-gas uniform distribution chamber 35A provide in the manifold part 
40 of each separator 11A via connection holes 36A in each separator 11A. 
The connection holes connects the oxidant gas introduction hole with the 
gas uniform distribution chamber 35A. The oxidant gas is led from the gas 
uniform distribution chamber 35A to the reaction part surrounding the 
manifold part via first gas communication hole 10C. 
A fuel gas is introduced into a gas uniform distribution chamber 35B 
through a fuel gas introduction hole 4 via connection holes 36B in each 
separator. 11A. The fuel gas is led from the gas uniform distribution 
chamber 35B to a reaction part surrounding the manifold part via second 
gas communication holes (not shown) arranged similarly to the first gas 
communication holes. 
The gas uniform distribution chambers 35A and 35B are arranged 
symmetrically on different main surfaces of the separator, respectively. 
The first and second gas communication holes are arranged on different 
main surfaces of the separator 11A, respectively. 
Other constructions are the same as the solid electrolyte fuel cell 
described in Embodiment 1 above. 
Since the reaction gases are distributed to the reaction part via the gas 
uniform distribution chambers 35A and 35B, uniformity in distribution of 
the reaction gases is improved and hence symmetry in reaction gas 
temperature distribution is improved, thus avoiding the occurrence of the 
thermal destruction of ceramics. 
Embodiment 5 
FIG. 9 is a cross sectional view taken along line 9--9 in FIG. 10 showing 
an example of the arrangement of a solid electrolyte fuel cell according 
to a fifth embodiment of the present invention. FIG. 10 is a cross 
sectional view taken along line 10--10 in FIG. 9. 
An oxidant gas is introduced through an oxidant gas introduction hole 5 and 
via gas communication holes 36C in the separator 11B into a gas uniform 
distribution chamber 35C, from which the oxidant gas is further led to the 
reaction part surrounding the manifold part via the gas flow hole 10E. 
A fuel gas is introduced through a fuel gas introduction hole 4 via gas 
communication holes 36D to the gas uniform distribution chamber 35D. The 
fuel gas is further led from the gas uniform distribution chamber 35D to 
the reaction part surrounding the manifold part through gas flow holes 
(not shown) but having the same construction as the first gas flow holes 
10E. 
The gas uniform distribution chambers 35C and 35D are arranged 
symmetrically on different main surfaces of the separator, respectively. 
The first and second gas flow holes are arranged on different main 
surfaces of the separator 11A, respectively. 
Other constructions are the same as the solid electrolyte fuel cell 
described in Embodiment 1 above. 
Since the reaction gases are distributed to the reaction part via the gas 
uniform distribution chambers 35C and 35C, uniformity in distribution the 
reaction gases is improved and hence symmetry in reaction gas temperature 
distribution is improved, thus avoiding the occurrence of thermal 
destruction of the ceramics. 
Embodiment 6 
FIG. 11 is an exploded perspective view showing an example of the 
arrangement of a solid electrolyte fuel cell according to a sixth 
embodiment of the present invention. FIG. 12 is a cross sectional view 
showing the solid electrolyte fuel cell shown in FIG. 12. 
As shown in FIG. 11, a unit cell 14 may be divided into a plurality of 
radially split segments. The unit cell 14 according to this embodiment 
consists of four radially spilt segments. Each segment is in the form of a 
sector with its tip portion being cut off along an arc of a concentric 
circle with the arc of the circle of the sector being as shown in FIG. 11. 
Unit cell 14 includes a cathode 14A, a solid electrolyte 14B, and a 
cathode 14C. 
The separators each have a central part and a reaction part surrounding the 
central part. The respective central parts of the separators serve as 
manifold parts in which there are formed gas introduction holes 4 and 5 
for introducing therethrough fuel gas and oxidant gas, respectively. The 
manifold parts of the separators have protrusions composed of a central 
disk portion and four ridge portions 50 radially extending from the 
central disk portion to the periphery thereof and arranged at right angles 
with respect to adjacent ridge portions. The protrusions are formed with 
grooves (not shown) for inserting the gas seal portion 6A (FIG. 2). The 
reaction part or region of each separator surrounding the manifold part 
thereof is formed with guide vanes 19A and 19B arranged on both surfaces 
thereof. The manifold part of each separator is formed with first gas flow 
holes (not shown) and second communication holes 10G having the same 
construction as the first gas flow holes but having a different height 
along the direction of the stack. The gas flow holes and communication 
holes are formed by drilling, and communicate with the gas introduction 
holes 4 and 5, respectively to lead fuel and oxidant gases to the guide 
vanes 19B and 19A, respectively. 
The electric insulator plate 21, which is a dense disk made of ceramic, is 
provided with two through holes that match or are aligned with the gas 
introduction holes 4 and 5, respectively. 
A fuel cell of the aforementioned type can be fabricated similarly to the 
solid electrolyte fuel cell of Embodiment 1, for example. 
An oxidant gas is introduced through an oxidant gas introduction hole 5 and 
via gas communication holes 36E in the separator 11C into a gas uniform 
distribution chamber 35E, from which the oxidant gas is further led to the 
reaction part surrounding the manifold part via the second gas flow hole 
10G. 
A fuel gas is introduced through a fuel gas introduction hole 4 via gas 
communication holes to the gas uniform distribution chamber (not shown). 
The fuel gas is further led from the gas uniform distribution chamber (not 
shown) to the reaction part of manifold part through the first gas flow 
holes (not shown) but having the same construction as the first gas flow 
holes 10G. 
The first and second gas uniform distribution chambers are arranged 
symmetrically on different main surfaces of the separator, respectively. 
The first and second gas flow holes are arranged on different main 
surfaces of the separator 11A, respectively. 
Use of the unit cell 14 in the form of a plurality of radially split 
segments is advantageous since not only is it easy to fabricate but it is 
also less susceptible to thermal damage. 
The unit cells may be those described in any one of Embodiments 2 to 9 
described above along as they are in the form of a set of sectors. 
The present invention has been described in detail with respect to 
preferred embodiments, and it will now be apparent from the foregoing to 
those skilled in the art that changes and modifications may be made 
without departing from the invention in its broader aspects, and it is the 
intention, therefore, in the appended claims to cover all such changes and 
modifications as fall within the true spirit of the invention.