Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-08-06
2001-06-12
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06245454
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell and relates more particularly to a fuel cell which has been improved to prevent a corrosion of a gas manifold due to phosphoric acid.
A fuel cell is used for generating electric energy based on an electrochemical reaction of hydrogen obtained by reforming a hydrocarbon fuel such as natural gas or methane gas with air as an oxidizer, both supplied to a main body of the fuel cell, in the presence of an electrolyte. The fuel cell has a laminated structure (a cell stacked structure) by a lamination of a plurality of single cells having the above-described power generating function.
FIG. 1
is a breakdown perspective diagram for showing the structure of a cell stack of a fuel cell which has been used conventionally. A single cell
1
of a fuel cell main body is structured by a fuel pole
3
for supplying hydrogen disposed at one side of the plane of a matrix layer
2
holding an electrolyte in the direction of an arrow A in the diagram, an air pole
4
for supplying air disposed at the other side of the plane in the direction of an arrow B in the diagram, grooved electrode materials
5
and
6
laminated on the fuel pole
3
and the air pole
4
respectively, and a separator
7
laminated on one of the grooved electrode materials
5
and
6
. Each time when the unit cell
1
is laminated to form a plurality of unit cells, a cooling panel
8
is inserted between each unit cell to structure one sub-stack
9
, and the sub-stack
9
is laminated by a large number to structure a cell stack
10
.
Further, a clamping panel
11
is installed at the top section and the bottom section of the cell stack
10
respectively. The cell stack
10
and the upper and lower clamping panels
11
are fastened by a tie rod
12
to be integrated as a cell stack unit
13
.
Further, a pair of fuel gas manifolds
15
a
and
15
b
and a pair of air gas manifolds
16
a
and
16
b
are disposed on mutually opposite side planes of the cell stack unit
13
of the above-described structure so that a fuel gas and air flow in mutually orthogonal directions, as shown in FIG.
2
.
Further, a gasket
18
is provided at each contact plane between the cell stack unit
13
and each of the gas manifolds
15
a
,
15
b
,
16
a
and
16
b
respectively to prevent in advance an occurrence of a problem of a reduction in the power generating efficiency due to a leakage of air or a fuel gas.
When fuel and air are supplied to the gas manifolds
15
a
and
16
a
respectively, a part of phosphoric acid impregnated in the matrix layer
2
and the grooved electrode materials
5
and
6
for structuring the cell stack
10
is diffused into the flow of the fuel gas and air respectively and is then exhausted to the outside of the cell stack (that is, into the gas manifolds) in the state of a phosphoric acid vapor.
However, since the temperature of the gas manifolds is slightly lower than the temperature of the cell stack, a part of the phosphoric acid vapor exhausted into the gas manifolds is condensed and adheres to the inner wall of the gas manifolds. When the fuel gas and air including phosphoric acid are brought into direct contact with the inner side of gas manifolds made of metal, the gas manifolds made of metal are corroded significantly in a high-temperature state, so that there is a risk that the gas manifolds soon have holes.
In order to eliminate the above-described drawback, a method of coating the inner plane of each gas manifold with a fluororesin as disclosed in the U.S. Pat. No. 4,950,563 has been used, as a method of protecting the gas manifolds from the corrosion by phosphoric acid.
However, the method of coating a fluororesin on the inner plane of the gas manifolds has the following problems and, therefore, it has been difficult to completely prevent the gas manifolds from being corroded by phosphoric acid.
According to the method of coating a fluororesin on the inner plane of a gas manifold, there has been a problem that phosphoric acid enters inside from pin holes and a problem that there occurs a failure in the adhesion of the resin coating on the inner surface of the gas manifold due to a repeated change in the temperature by the starting and stopping of the operation of the fuel cell and changes in the load since the coefficient of linear expansion of the resin coating is as large as about ten times that of the gas manifold, which results in a removal of the coating from the surface of the gas manifold.
Further, there is a problem that since a paint film formed by coating has a relatively small thickness, phosphoric acid can easily penetrate into the paint film, which results in a corrosion of the base material. Thus, this method lacks in reliability. Further, in order to improve the reliability of the coating, it is necessary to increase the thickness of the paint film, which requires a repetition of heating, coating and cooling processes many times. This requires a large processings time and a large number of processing. Moreover, since the coating process forms a part of a series of the manufacturing process of the gas manifold, these increases in the processing time and the number of processings have interfered to reduce the manufacturing period.
Furthermore, if the coating is broken and peeled off during the operation of the fuel cell, it is not difficult to detect this occurrence in a short time. This further has a problem of generating a corrosion of the gas manifolds and a failure of electric insulation.
BRIEF SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a fuel cell which is excellent in being phosphoric acid proof and electric insulation and which has a sufficient corrosion proof over a long period.
It is a second object of the present invention to provide a fuel cell in which a breaking of a lining can be prevented.
It is a third object of the present invention to provide a fuel cell which has a means for confirming the soundness of a lining.
It is a fourth object of the present invention to provide a reliable method of installing linings on gas manifolds of a fuel cell.
In order to achieve the above-described objects of the present invention, a fuel cell described in claim
1
of the invention has linings formed loosely on the inner phase of manifolds disposed on a side planes of a cell stack unit structuring the fuel cell, each lining having been formed by a phosphoric acid proof resin sheet by matching it with the shape of the inner plane of each gas manifold, wherein each lining is formed in advance to have a shape smaller than that of the inner plane of each gas manifold by a size substantially corresponding to the size of a thermal expansion of the lining during the operation of the fuel cell.
According to the invention having the above-mentioned structure, since the whole inner plane of a gas manifold can be covered with a lining formed by a phosphoric acid proof resin sheet that has been formed to match the shape of the inner plane of the gas manifold, it is possible to prevent the base material of the gas manifold made of metal from being corroded by phosphoric acid. Further, since the lining can be formed in advance to match the shape of the inner plane of the gas manifold, it becomes possible to manufacture the lining in a process different from the manufacturing process of the gas manifold, so that the period of manufacturing can be reduced.
Further, even if the lining has swollen due to an increase in the temperature of the inside of the gas manifold, it is possible to prevent the lining from being applied with a load that generates a crack because the lining matches the size and shape of the gas manifold.
The invention provides a fuel cell, wherein the phosphoric acid proof resin sheet for structuring the lining is either a PTFE (perfluoroalkoxyethylene-tetrafluoroethlene copolymer) resin sheet or an FEP (hexafluoropropylene-tetrafluoroethylene copolymer) resin sheet.
Further, the invention provides a fuel cell, wherein the phosphoric acid proof resin sheet for structuring the lini
Abiru Yoshiyuki
Gocho Yoshitsugu
Iyasu Kotaro
Konno Toshio
Kabushiki Kaisha Toshiba
Kalafut Stephen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ruthkosky Mark
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