DE102005024418A1 - Bipolar plate for fuel cells - Google Patents

Abstract

The present invention relates to bipolar plates for fuel cell stacks, comprising an electrically non-conductive substrate plate with opposite surfaces, each containing a partial surface and these partial surfaces have channels for gas transport, and at least one electrically conductive film, which is fixed on the non-conductive substrate plate, in that the partial surfaces of the opposite surfaces of the non-conductive substrate plate are covered by the at least one conductive film, and wherein the film has perforations in the region of the partial surfaces. Furthermore, the invention relates to methods for producing such a bipolar plate and fuel cell stacks containing the bipolar plates according to the invention, and their use in mobile and stationary devices.

Description

The The present invention relates to a bipolar plate and to the production thereof and fuel cell stacks containing these bipolar plates as well their use.

So far In particular, in motor vehicles predominantly internal combustion engines used to drive, the petroleum products as fuel require. Because resources are limited to oil and the products of combustion have an adverse environmental impact can, In recent years, research has been increasingly looking for alternatives Operated drive concepts.

The Use of electrochemical fuel cells for mobile and stationary power supplies finds increasing interest. Fuel cells are energy converters, convert the chemical energy into electrical energy. In the fuel cell the principle of electrolysis is reversed.

Currently exist different types of fuel cells, their principle of operation generally on the electrochemical recombination of hydrogen and oxygen based on the final product water. They relax Type of conductive used Electrolytes, the operating temperature level and achievable power ranges classify. For Automotive applications are Polymer Electrolyte Membrane (PEM) fuel cells particularly suitable. They usually become operated at a temperature in the range of 50 ° C to 90 ° C. Because the electric Voltage of a single cell for Practical applications are too low, need more of such cells connected in series to a fuel cell stack or stack become. Currently, PEM fuel cells typically deliver in the complete stack electrical services in the range of 1 to 75 kW (cars) and up to 250 kW (commercial vehicle, bus).

In a PEM fuel cell is the electrochemical reaction of Hydrogen with oxygen to water by the insertion of a proton-conducting membrane between the anode and the cathode electrode divided into the two substeps reduction and oxidation. in this connection there is a charge separation, which are used as a voltage source can.

A single PEM fuel cell has a symmetrical structure. A polymer membrane is followed on both sides by a catalyst layer and Gas distribution layer followed by a bipolar plate. current collectors serve to pick up the electrical voltage while end plates the addition of the reaction gases and removal of the reaction products to ensure.

• – chemische Beständigkeit gegen feuchte oxidierende und reduzierende Bedingungen;
• – Gasdichtheit;
• – hohe Leitfähigkeit;
• – geringe Übergangswiderstände;
• – Maßhaltigkeit;
• – Niedrige Kosten in Bezug auf Material und Fertigung;
• – Gestaltungsfreiheit;
• – hohe mechanische Belastbarkeit;
• – Korrosionsbeständigkeit;
• – geringes Gewicht.

In a fuel cell stack, a plurality of cells are stacked in electrical series with each other separated from each other by an impermeable, electrically-conductive bipolar plate, referred to as a bipolar plate. The bipolar plate connects two cells mechanically and electrically. Since the voltage of a single cell is in the range of 1 volt, it is necessary for practical applications to switch numerous cells in series. Often, up to 400 cells are stacked separately by bipolar plates. The cells are stacked in such a way that the oxygen side of one cell is connected to the hydrogen side of the next cell via the bipolar plate. The bipolar plate fulfills several functions. It serves for the electrical connection of the cells, for the supply and distribution of reactants (reaction gases) and coolant and for the separation of the gas spaces. A bipolar plate should fulfill the following characteristics:

• - chemical resistance to moist oxidizing and reducing conditions;
• - gas tightness;
• - high conductivity;
• - low contact resistance;
• - Dimensional accuracy;
• - Low costs in terms of material and manufacturing;
• - freedom of design;
• - high mechanical load capacity;
• - corrosion resistance;
• - low weight.

Currently Different types of bipolar plates are used.

bipolar plates made of graphite by pressing or milling be brought into the appropriate form. They are characterized by chemical resistance and low contact resistance, but have an insufficient mechanical behavior.

Composite materials are made of special plastics containing conductive fillers, based on carbon, for example.

One such composite material is described for example in FR-A-2,765,723.

At the common Bipolar plates consist of composites, but are also bipolar plates made of metal such as stainless steels, optionally coated could be, in use.

These metallic bipolar plates are characterized by high gas tightness, dimensional accuracy and high electrical conductivity. Due to the high requirements in terms of corrosion resistance, such bipolar plates, which include a metal plate, must be protected by appropriate measures. A disadvantage of such plates is in particular their high weight.

GB-A For example, 2359186 describes a metallic bipolar plate, which has a layer of electrically conductive polymer on its surface. This polymer should have sufficient resistance to the ensure electrochemical reaction conditions.

USA 2004/0081879 describes a fuel cell bipolar plate, the consists of a metallic substrate or a composite, the a conductive contact layer of noble metal with a thickness in the sub-micron range having.

USA 5,798,188 describes a bipolar plate comprising an aluminum plate includes, applied to the projections of a polymer and coated with a layer of metal, metal nitrite or metal carbide are.

In US 2003/0228512 discloses a stainless steel bipolar plate, in the substrate is made of stainless steel with a less than 100 nanometer thick conductive layer of a noble metal coated is.

WO-A 97/50139 describes a bipolar plate consisting of a polymer frame which is a carbon plate or other corrosion resistant conductive plate is poured.

Farther WO-A 01/28020 describes a bipolar plate comprising a metal plate which has a graphite emulsion layer and a graphite foil protected against corrosion is.

In US 2004/0038104 a bipolar plate is proposed which consists of a Chromium-nickel alloy which has the required corrosion resistance.

Finally describes DE-A10039674 a bipolar plate with a metal layer, the with non-conductive Plastic layers is enclosed, wherein the metal layer with their surfaces one or more electrically conductive compounds.

Farther Bipolar plates are proposed in the prior art, the no Metal or graphite base plate include. Here in particular plastics are used, the however, they must be modified to the required electrical conductivity of the bipolar plate guarantee.

Of the Advantage of the use of such polymeric base plates or substrates in bipolar plates lies in their resistance and low weight.

DE-A 19823880 discloses a bipolar plate made of thermoplastic material, which by electrically conductive Ink pen, such as. Carbon powders which are added to the thermoplastic, as well as a thin one Film of a conductive material, which, for example, by thin-film vacuum deposition on its surface is applied, is made electrically conductive.

DE-A 10261483 discloses a bipolar plate made of a thermoplastic or thermosetting polymer in which a metallic fabric is so incorporated is that existing on both sides of the surface channels the so-called "flow fields" of this tissue are covered.

adversely to the latter alternatives is the sometimes expensive Modification of the plastic substrate to provide adequate electrical conductivity to create.

The The object of the present invention is therefore a bipolar plate which is based on a non-conductive substrate, which is made electrically conductive in a simple manner.

• – eine elektrisch nicht leitfähige Substratplatte mit gegenüberliegenden Oberflächen, die jeweils eine Teilfläche enthalten und diese Teilflächen Kanäle zum Gastransport aufweisen und
• – mindestens eine elektrisch leitfähige Folie, die derart auf der nicht leitfähigen Substratplatte fixiert ist, dass die Teilflächen der gegenüberliegenden Oberflächen der nicht leitfähigen Substratplatte von der min destens einen leitfähigen Folie bedeckt sind und wobei die Folie im Bereich der Teilflächen Perforierungen aufweist.

The object is achieved by a bipolar plate for fuel cell stacks containing

• - An electrically non-conductive substrate plate having opposite surfaces, each containing a partial surface and these partial surfaces have channels for gas transport and
• - At least one electrically conductive film which is fixed on the non-conductive substrate plate such that the partial surfaces of the opposite surfaces of the non-conductive substrate plate are covered by at least one conductive film and wherein the film has perforations in the region of the partial surfaces.

It was in fact found that by simply coating of the channels for gas transporting surfaces (Flow fields) of the substrate plate with an electrically conductive foil a simple and inexpensive producible bipolar plate can be produced, wherein the electric Lead from one side of the bipolar plates to the other through both Side wrapping film is effected.

Preferably consists of the non-conductive substrate plate from a thermoplastic or thermosetting polymer.

in the The scope of the present invention is defined by the term "electrical not conductive "to understand that no or only negligible low electrical conductivity is available.

When Plastic material can all reinforced and unreinforced thermoplastic or thermosetting plastics are used, the against moisture oxidizing and reducing conditions, such as for example, prevail in PEM fuel cells, chemically stable are. In addition, they should be gas-tight and dimensionally stable. Examples of suitable Materials are PA, PBT, PPO, PP, PES, EP, UP, PF and others technical used plastics.

According to the invention can Flow fields of the substrate plate covered by an electrically conductive foil be. This is most easily achieved by placing a film over a outer edge the substrate plate out is and at least so far covers the substrate plate that the flow fields are covered by the film. Likewise, several slides can be used which overlap if necessary gas and liquid tight with each other to be connected.

The Foil has perforations in the area of the covered flow fields on. These serve to ensure that the gas components that are routed to the flow fields finely distributed through the perforations to the electrolyte, preferably a polymer electrolyte membrane (PEM), pour can.

The However, bipolar plate can also be designed such that the conductive Film through a gas-tight closed recess in the substrate plate outside the flow fields is recorded. Here, the recess is expediently dimensioned such that there is a film width, the one complete Covering the flow fields allows. Such a configuration corresponds to that as described in DE-A 10261483 is proposed, wherein here. but instead of the fabric the foil enters. This proposed variant can also be combined with the one when the film over an edge of the substrate plate is performed, be combined.

The Cover the flow-fields by bending the foil on the edge the recess towards the flow fields on both sides of the Bipolar plates done.

Farther can also over a film several edges or by a plurality of recesses in the substrate plate guided be. This will cause the conductivity elevated.

As well it is possible, that the film over three or four edges of the substrate plate and / or recesses in the substrate plate out becomes.

alternative can Also, several films are used, optionally on their impact edge be connected accordingly.

The electrically conductive Contains foil preferably carbon, a metal or a metal alloy. Preferably, nickel (pure), nickel alloys and high alloy To call steel. Here are the most important alloying elements for the steel Al, B, Bi, Co, Cr, Cu, La, Mn, Mo, Ni, Pb, Se, Si, Te, V, W, and Zr.

Around a break or a tearing the electrically conductive Film when bending over, for example, the edges of the substrate plate To avoid a tape or it may be several tapes on the Foil applied.

It is also the combination of two or more different Foil materials possible. When using a graphite foil, for example, for the improvement the electrical conductivity from one side of the bipolar plate to the other additional metal sheets U-shaped around an edge or several edges or through the designated Be performed recess or recesses.

The conductive film according to the invention preferably has a thickness in the range of 50 microns to 700 microns, more preferably in the range of 100 μm up to 500 μm and in particular in the range of 200 microns to 400 microns, on. As stated above, is the film partially provided with a perforation after application the slide over the flow fields is localized. The dimensioning of the perforation openings corresponds Advantageously, the channel width. To ensure the gas transport At least part of the perforation openings must be located above the channels of the flow fields be.

The Film can by various ways known to those skilled in the art Substrate plate to be fixed. This is particularly advantageous Fixation by gluing. This will be a particularly simple Type of preparation of a bipolar plate according to the invention allows.

to Gluing can common Adhesives are used. However, this should be considered be that the adhesive has sufficient resistance to the used operating fluids and against the operating temperature.

• – Bereitstellen einer elektrisch nicht leitfähigen Substratplatte mit gegenüberliegenden Oberflächen, die jeweils eine Teilfläche enthalten, und diese Teilflächen Kanäle zum Gastransport aufweisen;
• – Fixieren mindestens einer elektrisch leitfähigen Folie auf der nicht leitfähigen Substratplatte derart, dass die Teilflächen der gegenüberliegenden Oberfläche der nicht leitfähigen Substratplatte von der mindestens einen leitfähigen Folie bedeckt sind, und wobei die Folie im Bereich der Teilflächen Perforierungen aufweist; und
• – gegebenenfalls gasdichtes Verschließen von Ausnehmungen in der Substratplatte zur Aufnahme der leitfähigen Folie.

Another object of the present invention is a method for producing a bipolar plate according to the invention enthal the steps tend:

• - Providing an electrically non-conductive substrate plate with opposite surfaces, each containing a partial surface, and these partial surfaces have channels for gas transport;
• - Fixing at least one electrically conductive film on the non-conductive substrate plate such that the partial surfaces of the opposite surface of the non-conductive substrate plate are covered by the at least one conductive film, and wherein the film in the region of the partial surfaces perforations; and
• - Optionally gas-tight closing of recesses in the substrate plate for receiving the conductive film.

The Substrate plate can be produced by injection molding. This allows a particularly flexible spatial Design, so that despite the simple manufacturing complex geometric Structures can be created.

The at least one electrically conductive Slide can - like mentioned above - preferably be fixed by gluing. Here is the to be glued Part of the surfaces the bipolar plate provided with a suitable adhesive. alternative can provide the foil or foil and bipolar plate with adhesive become. Subsequently the foil is wrapped around the outer edge the bipolar plate and / or the inner edge (s) of the recess (s) bent and to the surface pressed the bipolar plate. If recesses are present, they must be sealed gas-tight, which is done by suitable adhesives can.

alternative can the film during the production of the substrate plate are encapsulated gas-tight, if the substrate plate contains a thermoplastic polymer to the gastight recording of the conductive To achieve foil in a recess.

One Another object of the present invention is a fuel cell stack from several fuel cells containing bipolar plates according to the invention.

The bipolar plates according to the invention are generally used in fuel cell stacks of multiple single cells. Such fuel cell stacks are formed by repeated stacking of bipolar plate, gas distribution layer, catalyst layer, polymer membrane, Catalyst layer and gas distribution layer produced. Between in each case two bipolar plates is present in a single cell. moreover become terminal Current collectors and end plates inserted. The layered ones Elements of the fuel cell stack are connected and sealed.

The Fuel cell stacks according to the invention can for example, for power supply in mobile and stationary facilities be used. In addition to a home care come in particular the power supply of vehicles, such as land, water and aircraft so like self-sufficient systems like satellites.

The Fuel cell stacks according to the invention are preferably in a temperature range of -40 to Stable at 120 ° C. The working temperature range is especially in the range around 80 ° C. The temperature can be achieved by suitable cooling media, the at least with a part of the stack in connection.

The bipolar plates according to the invention combine a beneficial combination of low weight, good electrical conductivity, Gas tightness and design of gas channels, as well as durability against corrosion.

Based of the figures, the present invention will be explained in more detail below.

It demonstrate:

1 an embodiment of a bipolar plate according to the invention prior to fixation of the electrically conductive film by corresponding bending, in which it is guided through a recess and

2 a further embodiment of a bipolar plate according to the invention prior to fixation of the electrically conductive foil by corresponding bending, in which it is guided around an outer edge of the bipolar plate.

According to 1 includes the bipolar plate 1 an electrically non-conductive substrate plate 2 , in the opposite surfaces each partial surfaces 3 (Flow fields), which have a variety of channels 5 exhibit. Furthermore, the electrically non-conductive substrate plate 2 Channels for the supply and removal of liquids and gases. About a first entrance 4 For example, H _{2 can be} supplied. The hydrogen is then distributed in fuel cell operation on the anode side via the channels 5 on the respective surface of the partial surfaces. The hydrogen not consumed for the fuel cell reaction is via the first output 6 discharged again. Likewise, there is a second input 7 and a second exit 8th for the other gas involved in the fuel cell reaction (eg, O ₂ ) passing through the (not in 1 visible) channels on the cathode side along the surface of the partial area, not shown on the back of the Bipolar plate is passed. Furthermore, the electrically non-conductive substrate plate 2 (not shown) have further channels for a coolant, which in the area of the partial surfaces 3 inside the bipolar plate 1 can be present. Furthermore, in the electrically non-conductive substrate plate 2 openings 9 included for mounting the bipolar plate 1 are provided in the fuel cell stack. In the in 1 illustrated embodiment of the present invention is the electrically conductive film 10 through a recess 11 guided, leaving the slide 10 in the direction of the faces 3 on the opposite sides of the bipolar plate 1 can be bent over. Preferably, a bond for fixing the film 10 in areas of the surface of the bipolar plate 1 instead of being outside the faces 3 on each side of the bipolar plate 1 lie. Furthermore, the film has 10 perforations 12 which are preferably located in the region of the film surface, after bending the film 10 on the faces 3 the opposite sides of the bipolar plate 1 to lie down. The electrically conductive foil 10 is dimensioned such that the opposing faces 3 completely after bending and fixing the film 10 are covered.

2 shows a further embodiment of a bipolar plate according to the invention 1 that in contrast to 1 but no recess for receiving a film 10 having. 2 shows an electrically conductive foil 10 at an outer edge 13 the bipolar plate is arranged. This is after bending the film 10 in the direction of the opposite partial surfaces 3 and subsequent fixation also a bipolar plate according to the invention 1 receive. Here is the slide 10 also dimensioned such that the opposite partial surfaces 3 the bipolar plate 1 after bending and fixing the film 10 completely covered by this and the fo lie 10 in the area of the partial surfaces 3 perforations 12 having. Furthermore, if necessary, the film 10 Have openings (not shown), which ensure that after bending and fixing the film 10 the openings 4 . 6 . 7 . 8th . 9 the bipolar plate 1 not from the slide 10 are covered.

As already stated above, both embodiments according to the 1 and 2 be combined with each other. There may also be further recesses and / or further outer edges of the bipolar plate 1 be used to guide the film or films.

Other conceivable embodiments are for example in the 4 and 5 DE-A 10261483 discloses, wherein instead of the fabric, the electrically conductive film 10 must be used according to the present invention.

1

bipolar

2

electrical non-conductive substrate plate

3

subarea

4

first entrance (H ₂ )

5

channels

6

first output (H ₂ )

7

second input (O ₂ )

8th

second output (O ₂ )

9

openings

10

electrical conductive foil

11

recess

12

perforations

13

outer edge

Claims (12)

Bipolar plate for fuel cell stacks comprising: - an electric non-conductive Substrate plate with opposite Surfaces, each one partial area contain and these subareas channels to have gas transport and - at least one electrical conductive Film which fixes on the non-conductive substrate plate is that the faces the opposite surfaces the non-conductive Substrate plate are covered by the at least one conductive film and wherein the film in the area of the partial surfaces Has perforations. Bipolar plate according to claim 9, characterized in that that the non-conductive Substrate plate is a thermoplastic or thermosetting polymer. Bipolar plate according to claim 1 or 2, characterized that the at least one conductive foil over at least an outer edge the substrate plate out is. Bipolar plate according to one of claims 1 to 3, characterized in that the at least one conductive foil by a gas-tight closed recess in the substrate plate outside of the partial surfaces is included. Bipolar plate according to one of claims 1 to 4, characterized in that the at least one conductive foil Contains carbon, metal or a metal alloy. Bipolar plate according to one of claims 1 to 5, characterized in that the at least one conductive foil has a thickness in the range of 50 to 700 microns. Bipolar plate according to one of claims 1 to 6, characterized in that the fixation by at least partially bonding of the film is done with the opposite surfaces of the non-conductive substrate plate. Bipolar plate according to one of claims 1 to 7, characterized in that additionally Metal sheets U-shaped around an edge or several edges or through the designated Recess or recesses led are. A method for producing a bipolar plate according to one of the claims 1 to 8, containing the steps - Provide an electrical non-conductive Substrate plate with opposite Surfaces, each one partial area contain and these sub-areas channels for gas transport exhibit; - fix at least one electrically conductive foil on the non-conductive substrate plate such that the faces the opposite Surfaces of the non-conductive Substrate plate are covered by the at least one conductive film and wherein the film has perforations in the region of the partial surfaces; and - possibly gas-tight closure of recesses in the substrate plate for receiving the conductive foil. A method for producing a bipolar plate according to one of the claims 4 to 8, containing the steps - Provide at least an electrically conductive foil, having the perforations; - Gas-tight encapsulation of Film for producing a thermoplastic electrically non-conductive substrate plate with opposite Surfaces that one partial area each contain and these subareas channels have gas transport; and - Fix the at least one electrically conductive foil on the non-conductive Substrate plate such that the faces of the opposite surfaces the non-conductive Substrate plate are covered by the at least one conductive film. Fuel cell stack of several fuel cells, the bipolar plates according to one of claims 1 to 8 contains. Use of fuel cell stacks according to claim 11 for power supply in mobile and stationary facilities.