The invention relates to a polar plate, particularly to an end plate or a bipolar plate, for a fuel cell comprising at least one flow field accessible from at least one side of the polar plate. The invention further relates to a termination and a repetitive unit for a fuel cell stack as well as to a fuel cell stack.
In SOFC fuel cell systems, for example, the fuel cell stack may consist of repetitive units stacked on top of each other as well as two termination units.
The membrane-electrode unit 26′ may, for example, be primarily formed of yttrium-stabilised zirconium oxide while the polar plate 10′ can be made of ferritic steel. Materials which are so different have different expansion coefficients which lead to stress during thermal cyclising (in an SFOC fuel cell system, for example, the temperature may vary between the ambient temperature and an operating temperature of 800° C. or more). Yttrium-stabilised zirconium oxide as well as ferritic steel are, in principle, capable of endure tension and pressure stresses without any plastic deformation. The three-dimensional structure of the polar plate 10′ which is recognisable particularly in
Deformations of repetitive units or termination units 30′ as shown in
The invention is therefore based on the object to at least substantially reduce deformations of termination and/or repetitive units for fuel cell stacks during a thermal cyclising.
Said object is solved by the features of the independent claims.
Advantageous embodiments and further developments of the invention are disclosed in the dependent claims.
The polar plate according to the invention is based on the generic state of the art in that at least one flow field is accessible via a plurality of access orifices. This solution is based on the finding that the material present between the access orifices results in a stiffening of the construction and, above that, to reduced bending moments when a plurality of small access orifices are provided instead of one large access orifice. In this way, as a result, the deformation of termination and/or repetitive units is at least considerably reduced which results in an enhanced cycle strength. Since the seals will no longer crack the tightness is enhanced. Since a breaking or sliding off of electric contacts is also prevented there is a reduced contact degradation in the entire fuel cell stack, i.e. of the contacts of anode and cathode, etc.
In preferred embodiments it is contemplated that the plurality of access orifices are separated from each other by at least one or more enforcement struts. It is, for example, possible to subdivide a large rectangular or quadratic access orifice into a plurality of smaller rectangular or quadratic access orifices by means of enforcements struts disposed perpendicular to each other. In this connection it is considered as particularly advantageous that the enforcement struts are formed by the material of a so-called blind plate as discussed later in more detail.
Furthermore, it is preferable that the polar plate according to the invention comprises a flow field plate comprising the at least one flow field and a blind plate comprising the plurality of access orifices. Similar to the state of the art the flow field plate and the blind plate are connected to each other in a gas-tight manner, for example by welding.
In preferred embodiments of the polar plate according to the invention it is contemplated that it consists, at least in portions, of steel, particularly of ferritic steel. Ferritic steel is, for example, capable of withstanding temperatures as they are encountered during the operation of SOFC fuel cell systems.
Furthermore, it is preferable that for the polar plate according to the invention at least one flow field for supplying a hydrogenous working gas to a membrane-electrode unit is provided. Similar to the state of the art the membrane-electrode unit may, for example, be primarily manufactured of yttrium-stabilised zirconium oxide.
In certain embodiments of the polar plate according to the invention it is contemplated that it is an end plate. For one of the end plates of a fuel cell stack it is sufficient that it comprises a flow field for distributing the hydrogenous working gas.
In other embodiments of the polar plate according to the invention it is contemplated that it is a bipolar plate and that distributor means for supplying an oxygenic gas to another membrane-electrode unit are provided on the side of the bipolar plate opposing the access orifices. The distributor means may, for example, be formed like a channel and attached to the side of the flow field plate opposing the flow field or formed integrally with the same.
The termination unit according to the invention for a fuel cell stack may, in particular, comprise:
a polar plate in the form of an end plate for a fuel cell stack comprising at least one flow field accessible from at least one side of the end plate via a plurality of access orifices, and
a membrane-electrode unit covering the plurality of access orifices, the at least one flow field being provided for supplying a hydrogenous working gas to the membrane-electrode unit.
The repetitive unit according to the invention for a fuel cell stack may, in particular, comprise:
a polar plate in the form of a bipolar plate for a fuel cell stack comprising at least one flow field accessible from at least one side of the end plate via a plurality of access orifices, and
a membrane-electrode unit covering the plurality of access orifices,
the at least one flow field being provided for supplying a hydrogenous working gas to the membrane-electrode unit and distributor means for supplying an oxygenic gas to a further membrane-electrode unit allocated to another termination or repetitive unit being provided on the side of the bipolar plate opposing the access orifices.
Furthermore the fuel cell stack according to the invention comprises:
at least one termination unit according to the invention, and
a plurality of the repetitive units according to the invention.
Preferred embodiments of the invention will be described by way of example in more detail with reference to the allocated drawings in which:
In the Figures the same or similar reference numerals designate the same or similar elements which will, for the avoidance of repetitions, at least partly only be explained once.
As is best recognisable by means of a comparison of
In
The cooperation of a termination unit 30 according to the invention and two repetitive units 34 according to the invention as well as another termination unit of another design which is not of particular relevance here can be seen in
The features of the invention disclosed in the above description, in the drawings as well as in the claims may be important for the realisation of the invention individually as well as in any combination.
Number | Date | Country | Kind |
---|---|---|---|
10 2006 016 814.3 | Apr 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/DE07/00621 | 4/5/2007 | WO | 00 | 6/26/2009 |