DE102010015504A1 - Gas diffusion layer for supplying reactant to electrode of membrane-electrode arrangement of polymer-electrolyte-membrane fuel cell of vehicle, has electrically conductive elevations containing amorphous carbon and/or graphite - Google Patents

Abstract

The layer has electrically conductive elevations through which channels (5) for reactants are defined together. The electrically conductive elevations contain amorphous carbon and/or graphite. The channels are formed between the elevations by mechanical, chemical and/or physical etching of carbon-containing base materials. The elevations comprise a base (10), which penetrates into a base body (3) of the diffusion layer. The elevations are provided in the form of rods (4). Independent claims are also included for the following: (1) a fuel cell of a vehicle, comprising a gas diffusion layer (2) a method for manufacturing a gas diffusion layer for a fuel cell of a vehicle.

Description

The The invention relates to a gas diffusion layer for a fuel cell, in particular of a vehicle, wherein the gas diffusion layer for Applying an electrode of a membrane-electrode assembly the fuel cell is formed with a reactant. The gas diffusion layer has a plurality of electrically conductive bumps, through which channels for the reactant from each other are delimited. Furthermore, the invention relates to a fuel cell with such a gas diffusion layer and a method of manufacturing a gas diffusion layer for a fuel cell.

The DE 10 2007 039 467 A1 describes a fuel cell with a gas diffusion layer, on the top of which are applied by physical vapor deposition, electrocoating or screen printing electrically conductive webs. The webs are formed from precious metals or metal oxides or doped metal oxides. In the fuel cell, the webs are brought into abutment with corresponding webs of a bipolar plate. A channel formed in the bipolar plate continues in the direction of the gas diffusion layer, where the channel is bounded laterally by the webs applied to the gas diffusion layer.

When The disadvantage of such a gas diffusion layer is the fact to see that the electrically conductive webs a Are subject to corrosion, especially when starting up and Switch off the fuel cell particularly high potentials. On the one hand, the corrosion leads to a mechanical obstruction the gas flow and on the other hand to an increased contact resistance between the bipolar plate and the gas diffusion layer. In addition is the application of the electrically conductive webs expensive and consuming.

task Therefore, it is the object of the present invention to provide a gas diffusion layer to create the type mentioned, which is simple and inexpensive is.

These Task is characterized by a gas diffusion layer with the characteristics of Patent claim 1, by a fuel cell with the features of claim 6 and by a method having the features of claim 8. Advantageous embodiments with expedient developments of the invention are given in the dependent claims.

The Gas diffusion layer according to the invention for a fuel cell, in particular a vehicle, is for applying an electrode of a membrane-electrode assembly of the fuel cell with formed a reactant. The gas diffusion layer has a A plurality of electrically conductive bumps, through which channels are delimited from one another for the reactant are. In this case, at least one of the electrically conductive Elevations of carbon. Carbon is particularly easy and inexpensive mountable. Preferably, all contain electrically conductive Elevations of carbon. In a gas diffusion layer having Fuel cells border the carbonaceous elevations to corresponding ones Webs on the separator plate. Here are the carbonaceous Elevations for a particularly low contact resistance between the gas diffusion layer and the separator plate. Though the carbon of the bumps may also be subject to corrosion, however, the oxidized carbon does not remain in the fuel cell, but this is discharged in gaseous form as carbon dioxide.

The electrically conductive surveys can in particular by partial removal of areas from a body be made of the gas diffusion layer, wherein the ablated Areas then form the channels. However, preference is given to the main body of the gas diffusion layer carbonaceous Material applied, from which the elevations are formed. However, the channels can also partially through Trough-shaped removal of the carbonaceous body the gas diffusion layer as well as partially by applying the carbonaceous Materials are realized on the body.

For a particularly effective supply of the electrode of the membrane-electrode assembly the fuel cell with the reactant is a particularly narrow and at the same time particularly deep channel advantageous. Especially when using metallic separator plates in the fuel cell However, the production of deep channel structures is one through the maximum possible deformation degree conditional limit set. Non-metallic, However, for example, graphitic separator plates have manufacturing technology and technical disadvantages. By using the present described gas diffusion layer for the fuel cell can be a channel with small width and large at the same time Depth also for separator plates formed from a metal be realized because a part of the channel bounded by the surveys is. A narrow, deep channel has a larger one through-flowable cross-section as an equal width Channel of lesser depth. Thus, the described with the present Gas diffusion layer provided fuel cell with a lower Starting pressure of the reactants are acted upon, since lower pressure drops and lower parasitic pressure losses during flow the channels occur.

The application of the electrically conductive, carbonaceous projections on the body of the gas diffusion layer also brings about an improvement in the mechanical properties of the gas diffusion layer. This makes it possible, as a base body for the gas diffusion layer, to resort to cost-effective, comparatively low-energy-producible rolled goods. Such rolled stock as a semifinished product for the gas diffusion layer can be formed from an impregnated graphite fiber fabric which is conditioned in a continuous process in a kiln. In contrast to a base body for the gas diffusion layer, which is formed of sheet material as a semi-finished product, the latter must be graphitized in a batch process at high temperature, which is particularly energy-intensive and thus expensive.

In an advantageous embodiment of the invention, the electrical conductive surveys at least partially made of amorphous Carbon and / or graphite formed. Especially amorphous carbon, about in the form of a carbon black paste, which on the body the gas diffusion layer is applied, is particularly inexpensive available, leading to a particularly cost-effective gas diffusion layer.

at a fuel cell, in particular for a vehicle, which has a gas diffusion layer according to the invention, is a membrane electrode assembly of the fuel cell over the gas diffusion layer can be acted upon by a reactant. in this connection are the electrically conductive bumps of the gas diffusion layer at least partially with corresponding surveys of a Separator plate brought into abutment.

A intended for use in a vehicle polymer electrolyte membrane fuel cell - in short PEMFC - can be structured as follows. The PEMFC contains the membrane electrode assembly - short MEA, which consists of a Anode, a cathode and an interposed polymer electrolyte membrane (also ionomer membrane or proton exchange membrane) - short PEM - is constructed. The MEA is in turn between arranged two separator plates, wherein the separator plate Has channels for the distribution of fuel and the other separator plate channels for distribution of oxidant and with the channels facing the MEA are. Such Separatorplatten therefore serve u. a. as distribution elements for the particular reactant. The channels form a channel structure, a so-called flow field.

The electrodes, anode and cathode, are generally designed as gas diffusion electrodes - in short GDE. These have the function of dissipating the current generated in the electrochemical reaction (eg 2H ₂ + O ₂ → 2H ₂ O) and allowing the reactants, starting materials and products to diffuse through. A GDE consists of at least one gas diffusion layer or gas diffusion layer - in short GDL - and a catalyst layer which faces the PEM and at which the electrochemical reaction takes place. The GDE may also have a gas distribution layer, which adjoins the gas diffusion layer and which faces in the PEMFC a Separatorplatte. Gas diffusion layer and gas distribution layer differ mainly in their pore sizes and thus in the nature of the transport mechanism for a reactant (diffusion or distribution).

A Such a fuel cell can operate at relatively low operating temperatures produce high-power electrical power. Real fuel cells are mostly to so-called fuel cell stacks - in short Stacks - stacked to achieve high power output wherein, instead of the monopolar separator plates, bipolar separator plates, so-called bipolar plates, are used and monopolar separator plates only the two terminal terminations of the stack form. They are z. T. end plates called and can structurally differ significantly from the bipolar plates.

The Bipolar plates are generally composed of two partial plates. These sub-plates have substantially complementary and with respect to a mirror plane mirror-image forms. The partial plates But they do not necessarily have to be mirror images. Important is just that they have at least one common touchpad have, where they can be connected. The partial plates point an uneven topography on. This results in the respective facing away from each other surfaces of the sub-panels already mentioned channel structures. At the respective consists of facing surfaces of the sub-panels z. B. in embossed metal part plates to the o. G. Channel structure complementary channel structure. When stacked of the two partial plates thereby arises between the partial plates, on their mutually facing surfaces, a cavity, which consists of a system of several interconnected tunnels consists. The cavity or the system of the tunnel is through a essentially the partial plates in the edge region circumferential joint framed liquid-tight, with openings to the Coolant supply and removal are provided so that the Cavity for the distribution of a coolant can be used.

Thus, the tasks of a bipolar plate include: the distribution of oxidizing agent and reducing agent; the distribution of coolant and thus the cooling (better tempering) of the fuel cell; the fluidic separation of the individual cells of a stack from each other; furthermore the electri cal contacting the series-connected single cells of a stack and thus the passage of the electric current generated by the individual cells.

A PEM can contain several components. The most important component is one or more proton-conductive ionomers. Furthermore, reinforcing components such. As organic fibers (especially PTFE fibers) and / or inorganic fibers (especially glass fibers) may be included, the z. B. may be formed as a woven or knitted fabric. Furthermore, fillers may be included, such as. B. metal oxide particles (especially silica gel, SiO ₂ ), the z. B. assume a function in the moisturization of the PEM. In addition, other components may be included, such as. As phosphoric acid, low molecular weight amphoteric (especially imidazole and / or pyrazole). However, a PEM can also consist of a proton-conductive glass film, in particular of a nanoporous phosphosilicate glass film. If a catalyst layer is applied to one or both of the main surfaces of the PEM, it is generally referred to as a catalyst-coated membrane-CCM for short.

at the gas diffusion layer according to the invention The fuel cell may have the channel depth of the flow field on the required for a desired pressure drop Depth to be adjusted. This is especially true when the separator plate Made of a metal, so very narrow channels Limits are set by the available forming processes.

at the inventive method for manufacturing a Gas diffusion layer for a fuel cell, in particular of a vehicle, the gas diffusion layer is for applying an electrode of a membrane electrode assembly of the fuel cell formed with a reactant. The gas diffusion layer is here with a plurality of electrically conductive elevations provided through which channels for the reactant be separated from each other. At least one of the electrically conductive Elevations is made from a carbon-containing base material educated. This can be achieved by applying the carbon Base material on a base body of the gas diffusion layer and / or by removing the channels from the body respectively.

The for the gas diffusion layer according to the invention and the fuel cell described advantages and preferred embodiments also apply to the invention Method.

The features and feature combinations mentioned above in the description as well as the below mentioned in the figure description and / or in the figure alone shown features and feature combinations are not only in the specified combination, but also usable in other combinations or in isolation, without to leave the scope of the invention.

Further Advantages, features and details of the invention will become apparent the claims, the following description is more preferred Embodiments and with reference to the drawing. This shows fragmentary and in a sectional view of a fuel cell for a vehicle.

A fuel cell shown in the figure 1 includes a membrane-electrode assembly 2 to which a basic body 3 adjacent to a gas diffusion layer. On the main body 3 are elevations in the form of webs 4 applied. Two bars each 4 border a channel 5 laterally. Through the channel 5 During operation of the fuel cell, a reaction gas flows, for example on one side of the membrane-electrode arrangement 2 Hydrogen gas and on the other hand oxygen-containing air. These reactants pass through the gas diffusion layer, reacting at the respective electrodes of the membrane-electrode assembly 2 to water and thereby generate electricity.

The bridges 4 are arranged so that they become surveys 6 which are complementary in a bipolar plate 7 are formed. Two adjacent surveys 6 the bipolar plate 7 border laterally and down a portion of the channel 5 off, which to the sides and up through the bars 4 and the main body 3 is limited. By doing that through the bipolar plate 7 formed channel structure in the gas diffusion layer is a particularly large depth of the channels 5 reachable. The one in the bipolar plate 7 formed area of the respective channel 5 can be a height 8th from 0.4 mm to 0.5 mm and a maximum width 9 from 0.7 mm to 0.8 mm. Starting from this maximum width in the area of the bipolar plate 7 In this case, the cross section of the channel tapers 5 in a direction away from the gas diffusion layer. The bridges 4 are trapezoidal in the illustrated example, wherein the shorter side of the trapezium of the bipolar plate 7 is facing. The channel 5 thus has a diamond shape in cross section. The channels 5 can in principle but also have other cross-sections, z. B. U-shaped cross sections or circular segment-shaped cross sections and the like.

The channels 5 between the electrically conductive webs 4 can either by structured application of the webs 4 on the main body 3 the gas diffusion layer can be made, or it can be applied to the main body 3 a carbon-containing layer are applied, from which then by mechanical and / or chemical and / or physi removing the ridges 4 be worked out.

This erosion may be by laser and / or electron beam and / or by a mechanical scraper or cutter or the like, and / or by chemical abrasion, such as by etching the areas in which the channels 5 to be trained. When applying separate webs 4 on the main body 3 can the carbonaceous web 4 be prepared by means of a doctor blade, a nozzle and / or in a screen printing process. As material for the bars 4 is suitable amorphous carbon, which in the form of a soot paste over the entire surface or already in the form of the webs 4 on the main body 3 can be applied. In addition or alternatively, graphite can be used.

Under physical abrasion is within the scope of the present invention understood: evaporation, heating, deformation, cracking by photons, Molding, melting, merging, coating, Spraying, and the like. This can be done, for example, by action of light or other radiation of all kinds (eg electron beams) done, z. B. with the help of UV lamps, diodes and the like. This z. B. Mask method, scanner technology, warm Forming tools, etc. are used.

When applying or working out and / or at least partially after the application or removal of the webs 4 These can be made hydrophilic or hydrophobic depending on the desired function. For example, the hydrophobicity of the webs 4 the hydrophobicity of the body 3 be adapted to the gas diffusion layer. By hydrophilic shaping of the webs 4 These can be like a wick to keep in the channels 5 forming water of reaction over the webs 4 is deducted and thus a sufficient gas supply to the electrodes of the membrane-electrode assembly 2 is guaranteed. This is particularly useful if the fuel cell 1 is operated with a comparatively high current density, which is accompanied by a comparatively high amount of water of reaction. Also by a hydrophobic design of the webs 4 can be achieved that water easily by means of the reaction gases from the webs 4 can remove and so the gas flow in the channels 5 hardly obstructed.

By hydrophilic forming the webs 4 they can serve to store water of reaction and so even in the absence or insufficient humidification of the reaction gases through a humidifier for a satisfactory humidification in the membrane of the membrane-electrode assembly 2 to care. Also, the bridge can 4 each have different interfacial tensions in its interior and on its surface, so that both the expulsion of water of reaction from the channel 5 and wicking simultaneously with a reservoir function of the lands 4 is feasible.

Also, by treating the main body 3 and / or the webs 4 or the soot layer from which the webs 4 be worked out by means of a laser, an electron beam, an infrared radiator, a drying device and / or a sintering device they are transformed so that there is a desired hydrophobicity, hydrophilicity, gas permeability and / or water permeability. Such a treatment of the main body 3 and / or the webs 4 may be by means of mechanical means, such as compaction means for three-dimensional patterning, roughening and the like, and / or by means of chemical means enabling roughening and / or modification of the surface and / or three-dimensional modification or structuring.

By treating the body 3 and / or webs 4 With the laser, the electron beam, an ionizing or Deionisiereinrichtung, and / or by mechanical or chemical means and / or by surface activation means, the penetration depth of the webs 4 into the main body 3 before and / or during and / or after their application to the base body 3 be set. If one the basic body 3 facing base 10 of the bridges 4 partially into the body 3 penetrates, can flow through the gas diffusion layer in the two-dimensional direction of extent and / or in the direction of the membrane-electrode assembly 2 be set down.

By the area in the body 3 penetrating base 10 can be ensured that out of the channels 5 into the main body 3 penetrating reactants perpendicular to the through the body 3 Move defined two-dimensional extension direction towards the electrodes and can escape laterally to a lesser extent. It is therefore the permeability in the two-dimensional direction of extent of the body 3 adjusted so that the pressure loss under the webs 4 is reduced, wherein the supply of reaction areas is improved with gases. This also leads to an improved discharge of water of reaction at high current density.

By causing short circuit flows of the fluids (fuel or oxidant) to adjacent channels due to penetration of the base 10 of the bridges 4 into the main body 3 are avoidable, more fuel or oxidant is available for the reaction. The penetration depth of the webs 4 into the main body 3 can be adjusted by treating the carbonaceous coating composition by laser, electron beam, ionizer, deionizer, physically, mechanically, chemically, and / or via surface activation methods before and / or during and / or after application of the coating composition. Likewise, these treatment methods for treating the body 3 are used and the properties of the body 3 Adjust so that the desired penetration depth of the webs 4 into the main body 3 is reached.

Furthermore, by the mentioned treatment methods, a particularly good electrical contact between the webs 4 and the bipolar plate 7 be achieved, as well as a particularly good adhesion of the webs 4 on the body 3 ,

1

fuel cell

2

Membrane electrode assembly

3

body

4

web

5

channel

6

survey

7

bipolar

8th

height

9

width

10

Base

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102007039467 A1 [0002]

Claims (8)

Gas diffusion layer for a fuel cell ( 1 ), in particular of a vehicle, wherein the gas diffusion layer for applying an electrode to a membrane electrode assembly ( 2 ) of the fuel cell ( 1 ) is formed with a reactant, and wherein the gas diffusion layer has a plurality of electrically conductive elevations ( 4 ), through which channels ( 5 ) are delimited from each other for the reactant, characterized in that at least one of the electrically conductive elevations ( 4 ) Contains carbon. Gas diffusion layer according to claim 1, characterized in that the electrically conductive elevations ( 4 ) are at least partially formed of amorphous carbon and / or graphite. Gas diffusion layer according to claim 1 or 2, characterized in that the channels ( 5 ) between the electrically conductive bumps ( 4 ) are at least partially formed by mechanical and / or chemical and / or physical removal of a carbonaceous base material. Gas diffusion layer according to one of claims 1 to 3, characterized in that the electrically conductive elevations ( 4 ) have a respective base which at least partially into one of the channels ( 5 ) limiting body ( 3 ) penetrates the gas diffusion layer. Gas diffusion layer according to one of claims 1 to 4, characterized in that the electrically conductive elevations ( 4 ) are at least partially hydrophilic and / or hydrophobic. Fuel cell, in particular for a vehicle, having a gas diffusion layer according to one of claims 1 to 5, and having a membrane-electrode arrangement ( 2 ), which can be acted upon via the gas diffusion layer with a reactant, wherein the electrically conductive elevations ( 4 ) of the gas diffusion layer at least in regions with corresponding elevations ( 6 ) a separator plate ( 7 ) are brought into contact. Fuel cell according to claim 6, characterized in that the separator plate ( 7 ) is formed of a metal. Method for producing a gas diffusion layer for a fuel cell ( 1 ), in particular of a vehicle, wherein the gas diffusion layer for applying an electrode to a membrane electrode assembly ( 2 ) of the fuel cell ( 1 ) is formed with a reactant, in which the gas diffusion layer with a plurality of electrically conductive elevations ( 4 ) through which channels ( 5 ) are delimited from one another for the reactant, characterized in that at least one of the electrically conductive elevations ( 4 ) is formed from a carbon-containing base material.