Fuel Cell Connector and Method of Using the Same

The present invention involves an electrically-conductive fuel cell electrode connector, the connector including an opening and a slot, the slot connecting an interrupted external edge of the connector to the opening to delimit a first flap and a second flap of the connector. A method of using the connector comprising a step of deforming the connector to be able to insert a module of unit cells into the connector opening.

DETAILED DESCRIPTION

For clarity, the same elements have been designated with the same reference numerals in the different drawings, which have been drawn out of scale. For clarity, only those elements which are useful to the understanding of the present invention have been shown and will be described. In particular, the forming of a unit cell of a fuel cell is known by those skilled in the art and will not be described.

FIG. 3is a perspective view of an electrically-conductive connector10for fuel cell electrodes. InFIG. 3, connector10is in a so-called initial position where it is substantially planar. The thickness of connector10may be in the range from 20 μm and 5 mm and, preferably, from 50 μm to 150 μm. The outer shape of connector10is for example substantially parallelepipedal. For example, connector10may be made of connection felt comprising metal fibers, for example, made of stainless steel. Thus, connector10is both permeable to gases and electrically conductive. The resistivity of connector10is for example in the range from 1×10−4Ω·cm to 5×10−2Ω·cm and preferably from 1×10−4Ω·cm to 5×10−3Ω·cm. Connector10is naturally deformable, substantially resilient, and rigid. It will be within the abilities of those skilled in the art to adjust, especially by successive trials, the composition and the preparation of the connection felt to optimize its physical parameters, in particular its rigidity and its resilience, with a view to using the connection felt in the context of the present invention.

Connector10comprises a felt11and an opening12, each of the two elements crossing the thickness of connector10.

Slot11connects an external interrupted edge13of the connector10to opening12to delimit a first element14and a second element15of connector10. It should be understood that slot11is open at its two ends.

According to an execution mode, the connector comprises first20, second22, and third24contact elements and first and second connection elements or arms21and23. The first and second contact elements form first and second flaps20,22. The first and second flaps are attached to the third contact element or base24by means of first21and second23arms, each of which is connected to base24. Preferably, connector10is in one piece, in other words, it may be formed from an adequately cut connection felt.

Opening12, for example, rectangular and located towards the central portion of connector10, is delimited and surrounded:for a first side of opening12, by a first internal edge25belonging to first contact element20and by a second internal edge26belonging to second contact element22;for second and third sides of opening12respectively extending at opposite ends on the first side, by a first internal side27belonging to first arm21and by a second internal side28belonging to second arm23; andfor a fourth side of the opening opposite to the first side, by a third internal edge29belonging to third contact element24.

In other words, opening12is delimited by: first25, second26, and third29internal edges of connector10respectively associated with first and second flaps20,22and with base24; first27and second28internal sides of connector10respectively associated with first and second arms21and23.

FIG. 4Ais a perspective view of a module30of two unit cells of a strip of cells for a fuel cell31, for example, planar. Module30comprises a first unit cell32and a second unit cell33partly forming fuel cell31. Module30comprises a fuel cell proton exchange membrane34. Membrane34is for example delimited by two substantially parallel surfaces. The equidistant points of the two surfaces of the membrane define a median surface45of planar fuel cell31. Membrane34comprises an upper surface35and a lower surface36located, in the example, on either side of median surface45. First unit cell32comprises a first pair37of electrodes facing each other and comprising a first upper electrode38located on the side of upper surface35of membrane34and a lower electrode39located on the side of lower surface36of membrane34. Second unit cell33comprises a second pair40of electrodes facing each other and comprising a second upper electrode41located on the side of upper surface35of membrane34and a second lower electrode42located on the side of lower surface36of membrane34. When connector10equips such a module, first upper electrode38is electrically connected to second lower electrode42by means of connector10.

Advantageously, an ionic and electric insulator surrounds the electrodes of unit cells32and33. For clarity, this insulator is not shown inFIG. 4A. The description of the electric and ionic insulator and of its use will be made hereafter in relation withFIGS. 5A and 5B. The unit cells have geometries generally used for fuel cells. For example, for a cell operating with dioxygen and dihydrogen, the thickness of membrane34is approximately 50 μm, and the thickness of the felt electrodes is approximately 250 μm. The electrodes have a surface area in the range from 0.3 cm2to 20 cm2. The distance between two adjacent electrodes located on a same side of membrane34is greater than 0.5 mm, and the distance between an electrode and each edge of membrane34is greater than 0.3 mm. All these dimensions are an illustration only and should not be considered as limiting the field of application of the present invention.

FIG. 4Bis a perspective view, in a position of insertion of connector10, previously described in relation withFIG. 3. In this example, connector10has been deformed to be installed on module30of two unit cells described in relation withFIG. 4A. First and second arms21and23are advantageously deformable to make first and second flaps20,22mobile with respect to base24. Thus, the first and second flaps may comprise a closed position and an open position (FIG. 4B) where the first and second flaps are more distant from each other than in the closed position.FIG. 4Bis a view of an example of an open position of the first and second flaps for which the distance between the two flaps20and22is sufficiently large to enable to introduce module30of two unit cells into opening12of connector10by using an enlarged passage, created by the deformation of connector10, between the spaced apart walls17,18of slot11.

FIG. 4Cis a perspective view of connector10, described hereabove in relation withFIGS. 3 and 4B, assembled on module30of two unit cells, described hereabove in relation withFIG. 4A. The method for assembling electrode connector10on module30comprises, for example, the steps of:forming an assembly30, for example of first32and second33unit cells described hereabove in relation withFIG. 4A;providing a connector10such as described in relation withFIG. 3;spacing apart walls17,18, delimiting slot11, to allow the introduction of assembly30of unit cells32,33between arms21,23;introducing assembly30of unit cells32,33into opening12from spaced apart walls17,18;bringing together spaced apart walls17,18after the introduction step;applying at least a portion of the first and second flaps on first upper electrode38located on upper surface35of membrane34; andapplying base24of connector10to second lower electrode42located on lower surface36of membrane34.

Connector10, assembled on unit cells32,33of module30of fuel cell31, is in a functional position which corresponds to the closed position of the first and second flaps. As compared with the position of insertion of connector10shown inFIG. 4B, the functional position of connector10is characterized, on the one hand, by the bringing together of first17and second18walls of slot11and, on the other hand, by the bringing together of first20and second22flaps. Further, for the functional position of connector10, that is, in the context of the unit cell module where first upper electrode38is electrically connected to second lower electrode42by connector10:first and second flaps20,22are applied to first upper electrode38of module30;base24is applied on second lower electrode42of module30;opening12of connector10is crossed by membrane34of unit cell module30;first21and second23arms are arranged on either side of membrane34.

In the example of a planar-type fuel cell31, the lower and upper electrodes are located on either side of median surface45. On each side of this median surface, membrane34is, for example, respectively supplied with the oxidizer—for example, dioxygen—and with the fuel—for example, dihydrogen. As a result, connector10achieves a series connection of two unit cells32,33mechanically connected by common proton-exchange membrane34.

FIGS. 5A and 5Bare respective top and front views of a module50, comprising a strip of four unit cells of fuel cell31, which is, for example, planar. Module50comprises, for example, the two unit cells32,33described hereabove in relation withFIG. 4A.

Module50of four cells comprises first32and second cell33, for example, in position two and three in the four positions occupied by the four cells of module50. Module50of four unit cells for example comprises proton-exchange membrane34common to the unit cells of module50. Membrane34defines median geometric surface45of planar fuel cell31configured to use module50of four unit cells. First32and second33unit cells are series-connected by connector10according to the description made hereabove in relation withFIG. 4C. Advantageously, connector10extends beyond the edges of the electrodes for which it provides a contact.

According to an execution mode applicable to all that has been described above, module30may comprise an ionic and electric insulator51arranged on the periphery of an electrode connected by connector10, the insulator simultaneously adhering to membrane34, to said connected electrode, and to connector10. Advantageously, insulator51extends beyond lateral edges52of membrane34. Advantageously, ionic and electric insulator51is in contact with the electrode edges, particularly with the edges of the first upper electrode38and of second lower electrode42connected by means of connector10. Advantageously, the three contact elements20,22,24of connector10cover, in a region bordering the electrodes of the connected cells, insulator51along a distance extending from each of the electrodes, for example, of at least 0.8 mm. Advantageously, the insulator adheres to:proton-exchange membrane34;electrodes38,42of the unit cells, as well as to the edges of these electrodes;connector10; andanother insulator of same nature.

For example, insulator51may be a polymer of thermoplastic elastomer type, such as a styrene-butadiene-styrene polymer known as SBS polymer. As an example, polymer “KRATON™ SBS D” produced by KRATON™ is suitable for the present invention. Other ionic and electric insulators may be used.

The method of manufacturing module50, of four unit cells connected by means of several connectors10, is for example described hereinafter. A first step comprises forming a strip of four unit cells comprising electrodes arranged on either side of fuel cell proton-exchange membrane34. A second step comprises depositing, on each surface of membrane34, a film of ionic and electric insulator51of thermoplastic elastomer polymer type, the film for example being cut with a shape contrary to that of the electrodes. Preferably, the thickness of the insulating film is substantially equal to the electrode height, for example, 250 μm. A third step comprises placing connector10, for example, made of connection felt, according to the method described hereabove in relation withFIGS. 4A,4B, and4C. A fourth step comprises compressing, preferably at high temperature, module50, provided with insulator51and provided with connector10, to apply contact elements20,22,24of connector10to electrodes38,42of the unit cells. The compression pressure is for example in the range from 2 kg·cm-2 to 20 kg·cm-2 and preferably from 8 kg·cm-2 to 12 kg·cm-2. The temperature, in the case of a hot compression, is sufficient to cause the melting of the thermoplastic elastomer polymer forming insulator51and, preferably, between 120° C. and 150° C. During this compression operation, insulator51is planarized and, preferably, flush with the electrode surface. Insulator51, during the hot compression operation, is placed in contact with the edges of the electrodes of the unit cells of module50. Consecutively to the hot compression operation, insulator51simultaneously adheres: to membrane34; to electrodes38,42connected by connector10; and to connector10, in particular in areas where connector10covers insulator51at the border of electrode38or42. As a result, connector10is glued to the periphery of the electrodes having connector10applied thereto. The connection felt of connector10is selected to be sufficiently rigid for the gluing to result in a force of application of the connection felt on the connected electrode, in order to provide a reliable electric contact. The gluing of insulator51to an insulator of same nature causes the encapsulation of proton-exchange membrane34by insulator51, deposited on each surface of membrane34and extending beyond edge52of membrane34. Thus, in particular, arms21and23of connector10, laterally located and at a distance from edges52of membrane34, are insulated from membrane34by ionic and electric insulator51. There is no risk of corrosion of the metal fibers contained in connector10.

Specific embodiments of the present invention have been described. Various alterations and modifications will occur to those skilled in the art. In particular, connector10may be used on a module comprising a large number of unit cells. The industrial manufacturing of fuel cells using connector10is eased since it is possible to provide an industrial process comprising, for example, three phases. During the first phase, strips comprising tens of unit cells interconnected by a proton-exchange membrane are formed. In a second phase, the electric connections are formed by means of connector10. Connector10may, according to cases, electrically connect electrodes located on either side, or on the same side, of the proton-exchange membrane (34). It is sufficient, in the case of a connection formed on electrodes located on a same side of median surface45, to apply connector10, in initial position with no deformation, on the electrodes. The same connector may thus form series or parallel connections of unit cells. Two unit cells interconnected by a same connector10are not necessarily consecutively placed on the strip of unit cells, since it is sufficient to adapt the dimension of the arms, in the longitudinal strip direction, to the distance between the unit cells to be interconnected. Finally, in a third phase, the strip provided with connectors10is sawn into modules, of a plurality of unit cells, forming the fuel cell to be achieved.

Besides, the electrodes have any shape, and the contact elements can then take an adequate shape to adapt to the electrode shape. Similarly, the shape of the slot or of an arm may vary, as long as they make the opening accessible by means of the connector deformation. The arm material should be deformable and electrically conductive, no matter whether or not it is made of the same material as the contact elements.

It is not necessary for the cells which are to be electrically interconnected to be mechanically interconnected. The presence of the opening for example enables to insert between an external mechanical element two different cells. The slot and the opening, associated with a deformable connector, then enable to install the connector despite the presence of this external element.