Contact Plate for Fuel Cells

Abstract

The present invention relates to a contact plate for fuel cells with a coherent active area (11) on at least one side of the contact plate, wherein the active area (11) consists of a contact surface (2) which over the whole surface comprises a coating (4) of an electrically conductive, corrosion-resistant material, and of recesses (3) so that the recesses (3) form a channel structure, wherein the coating (4) furthermore at least in the bottom regions (5) of the recesses (3) is omitted. The invention further relates to a corresponding fuel cell or to a fuel cell stack with at least one such contact plate as well as to various methods for manufacturing such contact plates which may serve as bipolar plates as well as monopolar plates or end plates. With the contact plate according to the invention, one achieves an optimally reduced contact resistance with a minimal material expense for the coating (4).

Description

One embodiment example of the invention is explained hereinafter by way of the FIGS. 1a and 1b. There are shown in

FIG. 1 a a cross section through part of a contact plate according to the invention and

FIG. 1 b a plan view of a bipolar plate composed of two such contact plates.

With the contact plate shown in FIG. 1a, it is the case one half of a bipolar plate for a fuel cell stack. In FIG. 1a one may recognise a plate body 1 which is manufactured of stainless steel. Corresponding embodiments of a different passivating and/or corrosion-stable metal are likewise possible. Directed towards the top in FIG. 1a, the contact plate has an active area which consists of a contact surface 2 as well as of recesses 3 which form a channel structure, wherein the contact surface 2 is interrupted by these recesses 3. The channel structure at the same times serves for the supply and removal of reactands or reaction products for a polymer electrolyte membrane contacting the contact surface 2, which is not shown here, or a diffusion layer or electrode lying between the contact plate and the polymer electrolyte membrane.

The contact surface 2 carries a coating 4 of platinum which covers the contact surface 2 over the whole area, but completely leaves free the recesses 3 with the exception of edge or transition regions which directly border the contact surface. In particular bottom regions 5 of the channel structure formed by the recesses 3 are free of the coating 4. The stainless steel from which the plate carrier 1 is manufactured, forms a passive layer there which in particular contains chromium oxide and which also protects the plate carrier 1 from corrosion where the active area which is only particularly coated has no coating. By way of the coating 4 of platinum, wherein also a different electrically conductive, corrosion-resistant material may be considered for the coating 4, a good electrical contact with a low contact resistance to an adjacent layer which is formed by a polymer electrolyte membrane or the corresponding diffusion layer or electrode is ensured. Such a contact would be prevented by the passive layer if the coating 4 were to be absent.

An edge region 12 of the contact plate which is shown in FIG. 1b and is outside the active area is likewise not coated, thus is left free of the coating 4. This simplifies a good sealing of the contact plate to the adjacent layer in this edge region 12.

By way of the embossing of a channel structure, the bipolar plate of the described embodiment example has an entire thickness of about 1 mm which corresponds to a channel depth of about 0.4 mm. The bipolar plate at the same time is formed by two parts of the type shown in FIG. 1a which are arranged on one another and are directed in opposite directions. Embodiments with which an additional layer is arranged between the two parts for achieving a greater stability or an increased thermal conductivity are conceivable. According to the part of the bipolar plate shown in FIG. 1a, also an end plate of a fuel cell stack or a monopolar plate may be designed for an individual fuel cell or several fuel cells arranged next to one another. The coating 4 with the shown embodiment example has a layer thickness of about 5 μm and is deposited with a surface density of about 10.6 g/m².

The coating 4 was deposited by pad galvanisation (tampon plating). In the same manner a manufacture of a coating of other galvanically pecipitatable substances would be possible, wherein in particular a coating with another precious metal such as gold would lend itself. With pad galvanisation (tampon plating), the plate carrier 1 itself serves as an electrode, whilst a second electrode which is surrounded by a material which is impregnated with a suitable electrolyte is led over the contact surface 2. By way of galvanic precipitation, the coating 4 then grows where the second electrode or the material surrounding it contacts the plate carrier 1 with the electrolyte, specifically at the contact surface 2, thus where the plate carrier 1 is raised. At the same time a wrapping of the second electrode of a non-woven may be provided as a material accommodating the electrolyte and surrounding the second electrode. A leaving-free of the recesses 3 during pad galvanisation (tampon plating) results also without any complicated prior masking of locations which are to remain free. Thus a partial coating of the contact plate also becomes possible in a quasi-continuous process with short cycle times. Also other lateral limitable coating methods such as spin-spraying, a use of slotted nozzles or printing methods may alternatively be used.

In particular one suitable embodiment of a contact plate according to the invention is possible with a coating 4 deposited by screen printing or roller printing, with which the coating 4 for example may be formed by way of a graphite-containing suspension or other suspensions or dispersions. By way of printing on a dispersion or suspension, in particular by way of screen printing or roller printing, onto the active area of the contact plate, likewise in a simple manner, a selective coating exclusively of the contact surface 2 may be achieved without a prior masking of the recesses 3 becoming necessary. An improved adhesion of the coating 4 on the contact surface 2 may be achieved on the basis of a thermoplastic or duroplastic polymer which melts or cross links on drying. A coating 4 which as with the embodiment example described by way of the figures is metallic may be realised as a material-saving conductor layer by way of printing a diluted metal dispersion onto the active area of the contact plate and subsequent melting, curing and cross linking onto the contact surface 2 of stainless steel.

Claims

1-11. (canceled)

12. A contact plate for fuel cells comprising: a coherent active area on at least one side of the contact plate, wherein said side is for contacting at least one of a diffusion layer, a fuel cell electrode and an electrolyte membrane; anda coating of an electrically conductive, corrosion resistant material;wherein said contact plate is constructed from passivating, corrosion-resistant metal;wherein said active area includes a contact surface and recesses, such that said recesses form a channel structure;wherein said coating includes carbon and one of a thermoplastic and a thermoset binding agent for depositing in liquid form, and said coating is disposed only on said contact surface of said active area.

13. The contact plate of claim 12, wherein said contact plate is constructed from one of a stainless steel and a titanium.

14. The contact plate of claim 12, wherein said coating extends over the entire said contact surface.

15. The contact plate of claim 13, wherein said coating extends over the entire said contact surface.

16. The contact plate of claim 12, wherein said contact plate further includes an edge region, said edge region being outside of said active area.

17. The contact plate of claim 13, wherein said contact plate further includes an edge region, said edge region being outside of said active area.

18. The contact plate of claim 14, wherein said contact plate further includes an edge region, said edge region being outside of said active area.

19. The contact plate of claim 12, wherein said carbon is in the form of graphite.

20. The contact plate of claim 12, wherein said coating further includes at least one of a niobium, a rare earth metal, a precious metal, a metal boride, a metal nitride, a metal carbide, a titanium nitride, a titanium carbide, a chromium nitride, and a silicon carbide.

21. The contact plate of claim 19, wherein said coating further includes at least one of a niobium, a rare earth metal, a precious metal, a metal boride, a metal nitride, a metal carbide, a titanium nitride, a titanium carbide, a chromium nitride, and a silicon carbide.

22. The contact plate of claim 12, wherein said contact plate has a material thickness between about 0.05 mm and about 0.5 mm.

23. The contact plate of claim 12, wherein said contact plate has a material thickness between about 0.07 mm and about 0.2 mm.

24. The contact plate of claim 12, wherein said contact plate is one of a monopolar and a bipolar plate.

25. The contact plate of claim 12, wherein said contact plate is an end plate.

26. The contact plate of claim 24, wherein said contact plate is an end plate.

27. A method of making a contact plate for fuel cells comprising the steps of: constructing said contact plate from a passivating, corrosion-resistant metal, a coherent active area on at least one side of said contact plate including a contact surface and recesses, said recesses forming a channel structure, said side being contactable by at least one of a diffusion layer, a fuel cell electrode and an electrolyte membrane; anddepositing a coating of an electrically conductive, corrosion-resistant material including carbon and one of a thermoplastic and a thermoset binding agent for depositing in liquid form upon said contact surface of the contact plate, said coating being disposed only on said contact surface.

28. The method of claim 27, further including the limitation of depositing said coating on said contact surface by one of a screen printing, a roller printing, and a metering method.

29. The method of claim 28, further including the limitation of the one of said screen printing, said roller printing, and said metering method being maskless at said recesses.

30. The method of claim 27, further including the step of heating said contact plate, said heating of said contact plate performs at least one of a melting and a curing of said coating.