WO2001093354A2

WO2001093354A2 - Polymer-electrolyte membrane (pem) fuel cell system and method for the production thereof

Info

Publication number: WO2001093354A2
Application number: PCT/EP2001/006175
Authority: WO
Inventors: Arthur Koschany
Original assignee: Manhattan Scientifics, Inc.
Priority date: 2000-05-31
Filing date: 2001-05-31
Publication date: 2001-12-06
Also published as: WO2001093354A3; AU2001267500A1

Abstract

The invention relates to a fuel cell system containing at least one polymer-electrolyte membrane (PEM) fuel cell with a polymer-electrolyte membrane (6) placed between a cathode catalyst layer (5) and an anode catalyst layer (7). The fuel cell also comprises gas diffusion layers (4, 8), which are located on both sides of the polymer-electrolyte membrane, and comprises at least one terminating layer (13), which rests against at least one of the gas diffusion layers. The fuel cell system is characterized in that the membrane (6), the catalyst layers (5, 7), the gas diffusion layers (4, 8) and the at least one terminating layer (13) of the fuel cell are, over their entire surfaces, joined to one another in a mechanically fixed, electrically conductive or electrochemically active manner by means of chemical bonding agents. The laminating processes are particularly suited for the use of PEM fuel cells in the mobile domain and for a planar configuration of the individual cells, in which a number of individual or double cells are adjacently located on a flat or curved surface.

Description

Fuel cell arrangement and method for its production

The invention relates to a fuel cell arrangement comprising at least one polymer electrolyte membrane (PEM) fuel cell with a polymer electrolyte membrane arranged between a cathode and an anode catalyst layer, gas diffusion layers arranged on both sides thereof and at least one closing layer adjacent to at least one of the gas diffusion layers, and on one A process for their manufacture, and specifically relates to high power density PEM fuel cells that are functional without external mechanical compression devices and are manufactured by lamination processes.

The central component of a PEM fuel cell is a polymer electrolyte membrane (PEM). It has the task that is typical of fuel cells

Reactants, e.g. B. hydrogen or methanol as fuel and air or pure

Separate oxygen as an oxidant, conduct H + ions and electronically isolate. Catalyst layers are applied to both sides of the membrane. Highly conductive porous layer materials and possibly additional channel structures are used to distribute the mostly gaseous reactants and to divert the electricity generated during operation. In these structures, the reactants are carried separately on both sides of the membrane. At least the fuel side must be sealed off from the surrounding air space by means of a gas-tight sealing layer or plate (e.g. a so-called bipolar plate) and a seal.

During operation of the cell, the

Membrane (anode) free of electrons and H + ions. On the opposite catalyst layer, the cathode, the electrons passed through an external circuit are combined with the H + ions traveling through the membrane and the oxidizing agent (e.g. oxygen from the air) to form the reaction product (e.g. water). This process creates a potential difference between the two catalyst layers that can be used in the outer circuit.

In order to obtain low electrical contact resistances between the individual layer materials, devices for mechanical compression perpendicular to the membrane surface of individual cells or stacks of cells are used in the prior art (cf. PCT / EP 00/03542 or US Pat. No. 5,484,666). Mechanical compression also serves to counteract the pressure force of the reactants (e.g. hydrogen), which are usually supplied with excess pressure. The compression device often consists of two solid plates screwed together, between which the fuel cell or the fuel cell stack is located. The pressure applied to the cells by these devices is typically between 5 • 10 ⁵ and 15 • 10 ⁵ Pa (5 and 15 bar). The high weight and volume of these plates and the associated costs are a decisive disadvantage for the practical use of fuel cells, particularly in the mobile sector. The most extreme are the effects of these plates on the power density of the fuel cells in planar arrangements in which a plurality of single or double cells are located next to one another on a flat or curved surface. In contrast to stack arrangements, the area of the clamping plates here is similar in size to the total active area of the cell arrangement.

With the present invention all disadvantages listed above can be overcome

Elimination of the mechanical compression devices can be avoided.

The invention is intended to create fuel power assemblies with a high power density without the use of mechanical compression devices, for which purpose simple and inexpensive lamination processes are preferably used to produce such fuel cell assemblies.

Starting from the fuel cell arrangement mentioned at the outset, this is achieved in that the membrane, the catalyst layers, the gas diffusion layers and the at least one end layer of the fuel cell are mechanically solid and electrically conductive or electrochemically active over the entire surface by ion-conducting chemical binders, in particular polymers and / or thermo - And / or thermosets, are connected to one another without the arrangement or the cell comprising a mechanical device compressing them, or in that during the manufacture of the cell the membrane, the catalyst layers, the gas diffusion layers and the end layer (s) of the Fuel cells are mechanically solid and electrically conductive or electrochemically active by means of ion-conducting polymers and / or thermoplastics and / or thermosets. The greatest advantages of the invention arise in the application fertilizer on planar arrangements of single and double cells.

The connection of layers, namely a polymer electrolyte membrane with two gas diffusion electrodes, by applying heat and pressure is known per se, e.g. B. from EP 0 935 304 A.

Preferred developments of the invention can be found in the respective subclaims.

Further details, advantages and developments of the invention result from the following description of a preferred embodiment with reference to the drawing. Show it:

1 shows a cross section through a single fuel cell. 2 shows a plan view of a planar arrangement of three fuel cells on a common substrate; Fig. 3 shows a cross section through a double fuel cell.

1, in a stack-like structure from bottom to top, consists of a substrate 1, an anode arranged on the substrate 1.

Current arrester 2, to which a carbon composite layer 3 is further connected and this in turn is connected to an anode gas diffusion layer 4. This layer 4 carries on its upper side in the drawing a catalyst 5 which lies directly against a membrane 6, the opposite side of which is covered by a layer 7 of a catalyst 7 on the cathode side. This layer is followed by a cathodic gas diffusion layer 8 on the side facing away from the membrane, on which narrow conductor tracks 9, possibly also only wires, are applied as current conductors. The anode gas diffusion layer 4 forms a gas space, which is sealed with the aid of a seal 10 and is supplied with combustible gas via a hydrogen inlet 11 Reaction products are discharged again via an outlet 12. The substrate 1, the anode current collector 2 and the carbon composite layer 3 together form a termination layer 13. In other embodiments, the termination layer may also consist only of the layers 2 and 3, or even only the current conductor 2.

Cells of the type shown in FIG. 1 can, for example, be arranged side by side in a planar manner on the substrate 1 on which the anode current conductors 2 are arranged with separating spaces 14. The connections of the individual parts of the anode current collector 2 are shown at 15; they are each connected to a star point of the cathode current conductor 9 for the purpose of connecting the three cells in series. The two current draw poles are marked with "+" and "-".

The individual cells have no through bolts or the like for pressing, but are glued together using suitable binders. By appropriately choosing these binders, the compressive strength of the arrangement is maintained despite a certain excess pressure in the anode gas diffusion layer 4.

The cells can also be assembled as a stack, for example as a double cell according to FIG. 3, which is mirrored on the substrate 1. Such cells are also constructed without mechanical pressing means.

In order to realize fuel cells of high power density without devices for mechanical compression, all the layer materials used must be mechanically stable and connected with a low electrical contact resistance. The compressive forces of the anode-side fuel (for example, hydrogen is assumed below) must be absorbed at least by the following interfaces (Fig. 1): Membrane 6 / catalyst layer 5 catalyst layer 5 / gas diffusion layer 4 gas diffusion layer 4 / closing layer 13

If the oxidant side is closed by means of a further sealing layer (air is assumed in the following as an example) and the cell is possibly operated with excess pressure, the analogous layer sequence must be mechanically connected. When the cathode is open, as shown in FIG. 1, these are the transitions

Membrane 6 / catalyst layer 7 catalyst layer 7 / gas diffusion layer 8 gas diffusion layer 8 / current conductor 9

Even under delaminating pressure loading by the hydrogen, a low contact and volume resistance must be guaranteed by the layer materials. The hydrogen pressures typically used are 10 ⁴ to 2 • 10 ⁵ Pa (0.1 - 2 bar). The described sequence of mechanically connected (laminated) layers can be used analogously for all common cell arrangements such as bipolar stacks, monopolar stacks, single cells and quasi monopolar double cells. For a special arrangement useless layers such. B. the substrate 1 for the inner cells of a bipolar stack can also be omitted.

The end layer has different functions in different cell arrangements. The requirements for gas tightness and conductivity parallel to the layer level are different. All requirements can be met by the finishing layer according to the invention, in particular according to Example 1. In the figures and the following description, channel structures for gas routing in the gas diffusion and / or closing layer are not explicitly discussed with the exception of example 1.

The end layer 13 comprises a material with an electrical conductivity parallel and perpendicular to the cell plane, which is sufficient to transport the electrical current produced during operation to the contact point 15 without a substantial drop in voltage. In order to avoid the use of expensive precious metals, which are the only metals that are chemically stable on the slightly acidic anode side, a continuous or slotted one is preferred

Non-precious metal foil (e.g. copper) is used, which is provided with a conductive, dense protective layer. The lamination method described in Example 1 is preferably used, which is based on a conductive, preformed layer material, as is known from WO 00/10174. For applications in which high mechanical stability against kinking of the cell surface is required, a metal foil can be fixed on a substrate that is as rigid as possible and has a low density. Glass or carbon fiber reinforced epoxy resin plates have particularly good properties. The easiest way is to use a continuous or partially copper-coated electronic board, which is available at very low cost due to mass production.

The membrane 6, the catalyst layers 5, 7 and the gas diffusion layers 4, 8 can be connected by hot pressing using an auxiliary polymer, preferably in a single operation to form the so-called membrane electrode assembly (MEA). The temperatures of up to 180 ° C (preferably up to 140 ° C) and pressures up to 5 • 10 ⁷ Pa (500 bar, preferably up to 250 bar) place high demands on the materials used. With regard to the pressure stability, unfilled commercially available carbon fiber papers (from Toray, Japan) are usually not suitable as a gas diffusion layer. Suitable very pressure stable gas diffusion layers are known from US Pat. No. 5,998,057. Improvements in this material with regard to tensile stresses perpendicular to the layer plane by introducing synthetic resins are set out in Examples 3 and 4 of WO 00/10174. These improved materials can be used not only as reinforcements for gas diffusion layers, as disclosed in this document, but also as complete gas diffusion layers.

As auxiliary polymers find Nafion ™ (Dupont), PTFE, THV ™ (Dyneon) and non-fluorinated thermoplastics such as. B. PE, PP and PS use. A suitable application of several of these polymers increases the adhesive force compared to the prior art and makes a significant contribution to the present invention. The polymers can be added in the form of powder, nonwovens, films, suspensions or solutions before the hot pressing of the gas diffusion and the catalyst layer. By applying the elevated temperature and pressure, these polymers melt or soften and combine

Layer materials intimately. Detailed procedures are described in Examples 2 and 3 below.

The conductive mechanical connection of the final layer and the MEA takes place, for. B. by applying a curable resin such as epoxy, furan or phenolic resin on the surface of the anode and / or on the surface of the final layer facing the anode. Curing is preferably carried out under pressure at elevated temperature.

To prevent the resin from blocking too much of the pores of the electrode, a microporous, conductive layer, e.g. B. be applied from carbon black, which absorbs the liquid resin during the curing process. Due to the larger capillary forces in the fine-pored layer, the resin penetrates the electrode only slightly. Alternatively, the hot pressing of the final layer and the MEA with a thermoplastic material positioned in between in the form of a film or a nonwoven leads to a firm, conductive connection.

The sealing of the free is also preferred with this method step

Membrane edge performed with the end plate. An adhesive seal with cold- or hot-curing silicones according to WO 00/02279 is preferably applied. According to DE 19703214 C, an adhesive seal without a free membrane edge can also be used with particular preference. Example 4 contains a detailed description of one of the methods.

The cathode current arrester shown in Fig.l only partially covers the cathode so that the oxygen in the air can diffuse to the catalyst. It preferably consists of a metal foil (for example copper) which is coated on one or both sides either with a noble metal or by the process in Example 1 (finishing layer). The current conductor is laminated to the cathode or the MEA analogously to the method for connecting the anode to the end layer.

Alternatively, the cathode current arrester can also be in the form of a grid or slotted

Metal foil is inserted between two cathodic gas diffusion layers during the reinforcement process mentioned above and then laminated in by means of an increase in pressure and temperature.

Example 1:

In the sense of Example 1 from WO 00/10174, a carbon fiber fleece (3 mg / cm ² ) with a dispersion of expanded, ground graphite, conductive carbon black and PTFE is impregnated one or more times by rolling in and dried after each impregnation step. The mass fraction of graphite based on the brought carbon materials is 10 to 100%, preferably 40 to 75%. The proportion of PTFE in the total solids introduced is about 3 to 10%. After drying and sintering, the total mass per unit area of the impregnated nonwoven is 6 to 25 mg / cm ² , preferably 8 to 14 mg / cm ² . This still porous layer material is covered with a solution of synthetic resin, e.g. B.

Epoxy resin, soaked in acetone and the solvents are evaporated. The proportion of synthetic resin in the solution is 10 to 90%, and preferably 40 to 60%. One or more of these nonwovens containing synthetic resin are placed on a copper foil or an electronic circuit board with exposed conductor tracks or a free but closed copper surface and, if necessary, increased

Temperature pressed until the resin is fully or partially cured. The resulting layer adheres well to the metal layer, is dense and has a low volume resistance and a low volume resistance to other carbon materials. Both resistors together are typically less than 40 mOhm • cm ² .

With regard to thickness and geometric structure, the conductor tracks on the electronic board can be designed in such a way that channels for guiding the reaction gases, in particular hydrogen, are formed. After coating, this channel structure is essentially retained.

Example 2:

The following layer sequence is pressed at 190 ° C for 15 seconds with a pressure of 10 ⁷ Pa (100 bar):

Gas diffusion layer polypropylene film 3.5 μm thick

Membrane coated on both sides with catalyst containing Nafion ™ or a related ionomer Polypropylene film 3.5 μm thick gas diffusion layer

A mechanically firmly connected and electrochemically active MEA is created. The above numerical data are only examples and can be subjected to large variations. Furthermore, other thermoplastics such as polyethylene can be used instead of polypropylene. In this case, the processing temperature can be significantly reduced.

A firm connection is also created if the gas diffusion layer, an additional layer on this gas diffusion layer or the catalyst layer contain powdered thermoplastics.

Example 3:

Two gas diffusion layers coated with catalyst on one side according to US Pat. No. 5,998,057 and a polymer electrolyte membrane coated on both sides with catalyst, e.g. B. Gore's PRIMEA ™ MEA. All catalyst layers are sprayed one or more times with a 0.5-5% Nafion ™ solution and then dried. In order to avoid corrugation of the membrane caused by the solvent, it is stretched on a fine-pored, non-metallic vacuum table during spraying and drying. The two gas diffusion layers face the catalyzed sides of the membrane, are positioned on both sides of the membrane and are pressed at about 140 ° C. with up to 3 · 10 ⁷ Pa (300 bar) pressure for about 2 minutes.

A mechanically strong bond is created.

Example 4:

The side of the end layer 13 facing the anode is covered with a sion of conductive carbon black, expanded graphite and PTFE in the 1: 1 mixed dispersion liquids isopropanol and water sprayed one or more times with intermediate drying. With regard to the total solids, the PTFE content is typically 3 to 10%. The mass ratio of graphite and conductive carbon black can be varied within wide limits. The dry mass of the spray layer is approximately 0.5 to 3 mg / cm ² . PTFE only serves as an auxiliary binder for the layer during processing.

A diluted synthetic resin (e.g. epoxy resin) as used in Example 1 is sprayed onto the previously described layer in a suitable amount. The solvents are then evaporated off. The sealing area of the later cell should be left out during both spraying processes.

As an edge seal for the cell, an adhesive bead made of thermosetting silicone is applied to the end layer on the circumference of the anode. The MEA is positioned exactly, placed on the final layer and hot pressed with it until the plastics have fully or partially cured. Typical pressures are in the range of 10 ⁶ to 3 • 10 ⁷ Pa (10 to 300 bar), the temperature depends on the requirements for curing epoxy resin and silicone.

The end product of this process step is a gas-tight, mechanically firm composite of MEA and final layer on the anode side. The cathode current arrester can be laminated afterwards.

Example 5:

A planar double cell according to FIG. 3 of basically known per se

Type (eg WO 95/17772) with connected anode spaces and two opposite cathodes is preferred with the help of a double-sided with metal coated electronic board built. The continuous or interrupted metal layers of the board are coated as described in Example 1 with a composite of polymers with different carbon materials. A double final layer is thus created. Membrane-electrode units with current arresters are attached and sealed on both sides of this layer using one of the methods mentioned above. A hydrogen inflow and outflow hole connects and supplies the two anode compartments. The top and bottom of this planar arrangement consist of cathodes. Since the metal layers of the two anodes are electrically insulated, the two cells can be connected in series, providing one for many

Applications require higher voltage.

Claims

Claims:

1. Fuel cell arrangement, comprising at least one polymer electrolyte membrane (PEM) fuel cell with a polymer electrolyte membrane (6) arranged between a cathode and an anode catalyst layer (5, 7), gas diffusion layers (4, 8) arranged on both sides thereof and at least one of the gas diffusion layers adjacent to at least one end layer (13), characterized in that the membrane (6), the catalyst layers (5, 7), the gas diffusion layers (4, 8) and the at least one end layer (13) of the fuel cell are mechanically strong and electrical conductive or electrochemically actively connected to one another over the entire area by chemical binders.

2. Fuel cell arrangement according to claim 1, characterized in that the binders are polymers and / or thermoplastics and / or thermosets.

3. Fuel cell arrangement according to claim 1 or 2, with a plurality of fuel cells arranged as a stack, characterized in that the cells of the stack are connected to one another by ion-conducting polymers and / or thermoplastics and / or thermosets.

4. Fuel cell arrangement according to one of claims 1 to 3, characterized in that the fuel cell has an end layer (13), which contains a continuous or interrupted metal layer (2), at least on the anode side with a layer (3) of carbon materials and thermoplastic and / or thermosetting plastic is provided.

5. A fuel cell arrangement according to claim 4 or claim 4, characterized in that several cells planar on one common final layer (13) are arranged.

6. Fuel cell arrangement according to one of claims 4 or 5, characterized in that the closing layer (13) has a substrate (1) which is stable against mechanical torsion.

7. Fuel cell arrangement according to claim 6, characterized in that the substrate (1) of the fuel cell consists of an electronic board with printed conductor tracks or with a continuous metal layer (2).

8. Fuel cell arrangement according to one of claims 3 to 7, characterized in that the end layer (13) on the one hand and the structural unit from the membrane (6), the catalyst layers (5, 7) and the gas diffusion layers (4, 8) on the other hand with thermal and / or thermosets are conductive and mechanically firmly connected.

9. Fuel cell arrangement according to claim 1 to 8, characterized in that the fuel cell has a cathodic current conductor (9) which with the structural unit from the membrane (6), the catalyst layers (5,

7) and the gas diffusion layers (4, 8) with thermoplastic and / or thermosetting plastic and mechanically firmly connected.

10. A method for producing a fuel cell arrangement according to one of claims 1 to 9, which has at least one polymer electrolyte membrane fuel cell with a polymer electrolyte membrane (6) enclosed between a cathode and an anode catalyst layer (5, 7) and gas diffusion layers arranged on both sides thereof ( 4, 8), characterized in that the membrane (6), the catalyst layers (5, 7), the gas diffusion layers (4, 8) and the end layer (s) (13) the fuel cell is mechanically fixed and electrically conductive or electrochemically active by ion-conducting polymers and / or thermoplastics and / or thermosets.

11. A method for producing a BrerinstoffzeUenanordnung according to claim

10, characterized in that the fuel cell is provided with an end layer (13) which contains a continuous or interrupted metal layer (2) which is provided at least on the anode side with a layer (3) made of carbon materials and thermoplastics and / or thermosets ,

12. A method for producing a fuel cell arrangement according to claim 10 or 11, characterized in that the fuel cell is provided with an end layer (13) which has a substrate which is stable against mechanical torsion.

13. A method for producing a fuel cell arrangement according to claim 12, characterized in that an electronic circuit board with printed conductor tracks or with a continuous metal layer (2) is used as the substrate (1).

14. A method for producing a fuel cell assembly according to one of claims 10 to 13, characterized in that the membrane (6), the catalyst layers (5, 7) and the gas diffusion layers (4, 8) of the cell with the ion-conducting polymers and / or the thermal and / or

Thermosetting bonds by hot pressing.

15. A method for producing a fuel cell arrangement according to one of claims 10 to 14, characterized in that the fuel cell is provided with an end layer (13) which is made with the structural unit the membrane (6), the catalyst layers (5, 7) and the gas diffusion layers (4, 8) by thermoplastic and / or thermosets preferably by hot pressing conductive and mechanically firmly connects.

16. A method for producing a fuel cell arrangement according to one of the

Claims 10 to 15, characterized in that the assembly of the membrane (6), the catalyst layers (5, 7) and the gas diffusion layers (4, 8) with a cathodic current conductor (9) is preferably carried out by thermoplastics and / or thermosets Hot presses are conductive and mechanically firmly connected.