DE102005032217A1 - Membrane electrode unit for electrochemical devices such as fuel cells and operating processes has ionomer membrane having through passage for internal air bleed function - Google Patents

Abstract

A membrane electrode unit for electrochemical devices comprises an ionomer membrane (1), at least one gas distribution substrate (4, 5), protective film and at least one catalyst layer (2, 3). The ionomer membrane comprises at least one through passage that enables internal transport of air from the cathode side to the anode side. Independent claims are also included for the following: (A) a fuel cell as above; (B) a fuel cell stack as above; (C) operation of a fuel cell as above.

Description

The The present invention relates to the technical field of electrochemistry and the fuel cells, in particular the field of membrane fuel cells, such as PEMFC and DMFC. It describes a membrane-electrode unit ("MEE"), the one or several bushings for one internal transport of air (or oxygen) from the cathode to the Anode has and a method for their operation. Membrane fuel cells and PEM stacks containing such membrane-electrode units can on simple way with contaminated hydrogen, methanol or with CO-containing reformate gas are operated, with very good performance be achieved.

fuel cells convert a fuel and an oxidant locally from each other separated at two electrodes into electricity, heat and water. As fuel can be hydrogen, a hydrogen-rich gas, but also methanol; serve as an oxidant oxygen or air. The process of Energy conversion in the fuel cell is characterized by a particularly high efficiency. For this reason, fuel cells win generally for mobile, stationary and portable applications increasingly important. In particular, the membrane fuel cells (PEMFC, DMFC etc.) are due to their compact design, their power density and their high efficiency for use in the above areas.

The core of a PEM fuel cell is the so-called membrane-electrode assembly ("MEE") .The membrane-electrode assembly is sandwiched and typically consists of five layers 1a , In this case, the anode gas distribution substrate forms (4) with the anode catalyst layer (2) the gas diffusion electrode ("GDE") on the anode side; the cathode gas diffusion substrate (5) with the cathode catalyst layer (3) forms the gas diffusion electrode ("GDE") on the cathode side These catalyst coated gas diffusion electrodes are also referred to as "catalyst-coated backings"("CCBs") The ionomer membrane (1) lies between the two GDEs. To fabricate a five-layer membrane-electrode assembly, anode GDE and cathode GDE are sandwiched with the ionomer membrane (hereinafter referred to as "CCB method").

In an alternative variant ( 1b ) are the catalyst layers (2) and (3) directly on the ionomer membrane (1) applied and form a so-called "catalyst-coated membrane"("CCM"). To produce a five-layered membrane-electrode assembly, this catalyst-coated membrane (CCM) is equipped with two uncatalyzed gas diffusion substrates (4) and (5) in turn, sandwiched together into a five-layered membrane-electrode assembly (hereinafter referred to as "CCM method.") Both methods ultimately result in a five-layered membrane-electrode assembly.

to Production of a PEM single cell is on the anode side, the associated anode bipolar plate with the gas supply channels and on the cathode side, the corresponding cathode bipolar plate with the associated Gas supply channels attached and this structure firmly put together. Through the gas supply channels (also called "flow-field") is the Supply and removal of the reactants in the membrane-electrode assembly ensured. Between the bipolar plates and the membrane or the membrane-electrode unit are often seals or protective films for gas-tight sealing. In the so-called fuel cell stacks ("stacks") are such single cells Stacked in any number and connected in series.

Preferably become PEM fuel cells with hydrogen and air as reaction gases operated. They deliver the best performance. Be DMFC directly with aqueous methanol operated. In the stationary However, fuel cell heating systems are mainly used in the area Reformatgas operated, which by reforming from natural gas or heating oil will be produced. Reformatgas consists of about 70-75 Vol .-% hydrogen and 20-25 vol.% carbon dioxide; contains in practice this gas also nitrogen and depending on the degree of purification changing Amounts of carbon monoxide (CO, up to 1% by volume), sulfur compounds and possibly odorants.

Also the commercially available Hydrogen is still with traces due to its manufacturing process contaminated by CO and hydrocarbons in the ppm range. there On the market hydrogen is available in different degrees of purity. Due to the trace amounts of CO can also be used in long-term operation the PEM fuel cell with such commercially available Hydrogen the poisoning effects described below occur.

When operating with hydrogen-containing gases that are contaminated by carbon monoxide, there is generally a loss of performance due to the poisoning of the platinum-containing anode catalyst. Conventional platinum catalysts are very sensitive to poisoning by carbon monoxide. Therefore, the content of the anode gas of carbon monoxide must be lowered to less than 10 ppm in order to prevent degradation of the fuel cell by a Vergif tion of the anode catalyst to prevent. This applies in particular to the PEM fuel cell, which, with its low operating temperatures (generally below 100 ° C.), is particularly sensitive to poisoning by carbon monoxide. Even with direct methanol fuel cells, adsorption of CO on the anode catalyst takes place intermediately.

The Problem of poisoning of platinum catalysts by carbon monoxide has been known for a long time. Carbon monoxide (CO) is due to its special molecular structure on the surface adsorbs the platinum and thus blocks the access of the hydrogen molecules of the anode gas to the catalytically active centers of platinum. In the catalyst layers on the anode and cathode side of the PEM fuel cell often Catalysts based on precious metals (i.e., metals of the VIII. Subgroup of the Periodic Table of the Elements) used. Preferably become Ru, Pt, Au, Pd or Ir alone or in combination with each other or in combination with base metals such as nickel, cobalt or manganese used. Electrocatalysts contain fine precious metal particles, on a conductive support material (usually soot or Graphite) are deposited. The content of precious metal is between 10 to 90 wt .-%, based on the total weight of the catalyst.

From the EP 924784 B1 It is known that the tolerance of a platinum catalyst to poisoning by carbon monoxide by alloying or doping of the platinum with other metals, for example with ruthenium (Ru), can be improved. As a result, the oxidation of the adsorbed on Pt carbon monoxide is achieved to carbon dioxide, which is then easily desorbed. The oxygen for this purpose is supplied either in the form of small amounts of air (hereinafter "air bleed") or in bound form as water to the anode gas stream.

The US 4,910,099 describes a method for preventing CO poisoning of the fuel cell electrode by injecting oxygen or air into the hydrogen stream above ("upstream") of the fuel cell The addition of air into the hydrogen stream takes place outside the PEM fuel cell or outside the PEM Fuel cell stack, ie before the hydrogen flow enters the fuel cell (so-called "external air bleed"). In contrast, in the present invention, the addition of air or oxygen takes place within a membrane / electrode unit, or within a PEM fuel cell (so-called "internal air bleed").

From the US 6,210,820 is a method for operating a PEM fuel cell with contaminated fuel gases is known in which air or oxygen is added discontinuously, for example in periodic pulses, the fuel gas. The addition of the oxidizing agent (air or oxygen) into the hydrogen stream takes place before it enters the fuel cell.

The DE 102 21 146 describes a PEMFC system for mobile applications, wherein the addition of the "air bleed" is also discontinuous, but after the end of the electrical power requirement to the fuel cell and is for example built into a shutdown cycle .Also, the addition of air or oxygen in the Hydrogen flow outside the fuel cell, ie before the hydrogen flow reaches the fuel cell.

all Embodiments described herein in common is that the addition of the oxidizing agent (i.e., air or oxygen) into the hydrogen stream before it enters the fuel cell, i. into the anode electrode of the fuel cell arrives. This principle, which represents the state of the art, becomes as "external air bleed ". To carry out the process are complex supply and control devices (valves, Pipes, pumps, sensors etc) necessary, which makes the system more complex shape and to additional performance degradation to lead. Furthermore leads this Procedure to increased Cost of the entire fuel cell unit.

It was therefore an object of the present invention, a membrane fuel cell or a membrane-electrode assembly for a membrane fuel cell provide with contaminated hydrogen, with contaminated hydrogen-containing fuel gases or operated with methanol can. Although the concept of "air bleed" for CO oxidation should be applied, However, this concept should be realized in a simple way and no extra and cause expensive external supply and control devices. Farther should be a simple method of operating membrane fuel cells with "air bleed "found become.

These Tasks are performed according to the invention the provision of a membrane electrode assembly according to claims 1 to 18 solved. The further claims refer to a membrane fuel cell containing these Membrane electrode units according to the invention and the method of operating a membrane fuel cell with internal air transport.

The The invention relates to a membrane electrode assembly for electrochemical Devices containing an ionomer membrane with front and back, at least one gas distribution substrate, at least one protective film and at least one catalyst layer, wherein the ionomer membrane at least one implementation having an internal air transport from the cathode side to the anode side allows.

there the addition of the oxidizing agent (air or oxygen) takes place to the hydrogen flow within a PEM single cell or within a membrane-electrode unit. This principle of internal air transport (hereinafter referred to as "internal air transport") air bleed ") is made possible by the provision of the membrane-electrode unit according to the invention, which at least one implementation for Transport of the oxidant from the cathode side to the anode side having.

It has been shown to be using one or more such implementations through the ionomer membrane or through the catalyst-coated Membrane (CCM) reproducibly air or oxygen from the cathode side (air side) to the anode side (fuel gas side) a membrane-electrode unit (or a single PEM cell) can be transported. By the "internal air bleed " an increased CO tolerance achieved when operating with CO-containing fuel gases and Furthermore the anode catalyst (usually a PtRu catalyst) regenerated.

Surprisingly is the already known "air bleed effect as well in the internal supply of air (i.e., directly by transport of the cathode side to the anode electrode of the membrane-electrode assembly) to observe. The inventors have found that the membrane-electrode unit according to the invention with implementation (s) and "internal air bleed "in Reformatbetrieb are quite resistant to aging and only a small degradation in long-term operation exhibit. Also with direct methanol fuel cells (DMFC), this principle is applicable, although the following versions refer to fuel gas powered cells.

The transport of the air through the passage (s) of the membrane-electrode unit can be effected, for example, by diffusion or by convection. The internal air flow can be regulated by the pressure difference (Δ p) between anode gas supply and cathode gas supply: Δp = p cathode - p anode (1)

Where: Δ p ≥ 0 (2) and preferably: Δp> 0 (3)

By the condition according to equation (3) prevents hydrogen-containing Fuel gas in larger quantities from the anode to the cathode side passes. This will be for example by different design of the anode and / or cathode gas supply channels ("flow fields") and / or by the setting of different volume flows achieved, creating a defined internal pressure drop between gas inlet and gas outlet on the Anoden- or cathode side of the cell is set. By the internal pressure drop over the "flow fields "arises a defined pressure difference (Δ p) at the site of the implementation (s) between anode and cathode side.

Of Further, the operation of the membrane electrode assembly or fuel cell according to the invention by means of "internal air bleed "either continuously or discontinuously (i.e., for example, pulsed). In pulsating operation of the cell, the pressure difference (Δ p), for example, via the applied anode gas or Cathode gas pressure can be controlled.

About the Adjustment of this pressure difference (Δ p) and, for example via the Positioning, type, number and diameter of the implementation (s) in the membrane-electrode unit Different parameters are available with which the type, the quantity and the amount of air flow from the cathode to the anode varies can be.

In In practice, the presence has at least one implementation in the membrane-electrode unit proven, but there are also - depending on the operation of the membrane electrode assembly according to the invention - others embodiments with several feedthroughs possible. As a rule, 1 to 10, preferably 1 to 5 lead-throughs present in the membrane-electrode unit. The inner diameter (d) the bushings is typically in the range of 5 to 5000 microns, preferably in the range of 10 to 1000 μm.

In a first embodiment, the feedthroughs are placed in the non-active region (ie, non-catalyst coated region) of the membrane-electrode assembly. Preferably, the membrane bushings are positioned in the region of the sealing surfaces or the protective film on the edge of the membrane-electrode assembly. The bushings can be lined or fixed with a suitable material, the lining having plastics such as thermoplastics, thermosets, adhesives or elastomers can and is formed for example in the form of plastic tubes, cannulas, sleeves or rivets.

By the fixation of the inner diameter (d) becomes a possible widening and prevents cracking in continuous operation. In some cases it is through the lining achieves that the catalyst layers are not in direct contact with the implementation. The described lining is optional and has the consequence that the inner diameter (d) of the implementation over the entire period of operation remains largely constant, whereby during operation a constant air flow guaranteed is. However, even without a lining when operating in the lower one Temperature range (i.e., in the range of 20 to 60 ° C) an increase in the Diameter of execution not to be expected.

An illustration of the first embodiment is exemplary in FIG 2 shown. The PEM single cell shown here consists of a seven-layer membrane-electrode assembly with an ionomer membrane (1) that a carry (9a) in the field of protective films (6) at the edge. The implementation (9a) is not lined in this case. It is in communication with the gas supply channels of the anode bipolar plate (7) and the cathode bipolar plate (8th) , This creates a channel for air transport from the cathode side to the anode side.

3 shows a PEM single cell containing a membrane electrode assembly according to the invention in a second embodiment. Here is the implementation (9b) mounted within the active area of the membrane-electrode assembly. The illustrated membrane-electrode assembly is in the CCM method (ie after 1b produced. Therefore, in addition to the ionomer membrane (1) also the catalyst layers (2) and (3) , which form the active area, perforated. The channel formed by the passage extends from the bottom of the cathode gas diffusion substrate (5) to the bottom of the anode gas distribution substrate (4) , The feedthrough is not lined and is not directly in communication with the gas supply channels of the anode bipolar plate (7) and the cathode bipolar plate (8th) , However, since the gas distribution substrates have good gas permeability, air transport from the cathode side to the anode side is enabled.

For membrane-electrode assemblies manufactured according to the CCB method (ie after 1a ), is only the ionomer membrane (1) perforated, carrying (9b) extends in this case to the lower sides of the catalyst layers (2) and (3) approach. Combinations between the various MEE types and MEE production methods are possible and can be used in a membrane-electrode assembly according to the invention.

In a further embodiment are the bushings within the active area the membrane-electrode unit. They are, however, of a border of non-active material (e.g., plastics such as Thermoplastics, thermosets, adhesives or elastomers). Preferably, the border of the passage consists of the material of Protective film.

4 shows a top view of a catalyst-coated membrane (CCM) with ionomer membrane (1) , Cathode catalyst layer (3) and protective film (6) , The implementation (9a *) is with a border of protective film material (6a) Mistake. The catalyst layers (3) and (4) have at this point a recess. The border can be placed on the front and / or on the back of the bushing. The border, whose shape and area is adapted to the dimensions of the implementation, a direct contact of the implementation is avoided to a catalyst layer. The border may be combined with a liner, both of which may be made of the same material. It is possible to consider such recesses, borders and linings already in the design of the membrane-electrode assembly.

In a further embodiment, one or more feedthroughs of the membrane-electrode assembly according to the invention have special devices with which the air transport of the "internal air bleed" can be regulated or interrupted.For this purpose, valve-like devices such as diaphragm valves can be used . packaging technology known Such valves may either be fitted a passage in the channel or attached to the input of an implementation at the anode or at the cathode side when creating a pressure difference (Δ p) between the cathode side and anode side (where Δ p = p _cathode. - p _anode > 0), the diaphragm valve opens and allows the cathode air to be transported to the anode, thus enabling a discontinuous "internal air bleed". On the other hand, if there is a higher anode gas pressure, the diaphragm valve remains closed and thus prevents transport of hydrogen-containing fuel gas to the cathode side.

If, for example, a somewhat higher pressure is applied to the cathode side, then the air transport from the cathode side to the anode side can be regulated. If the cathode gas pressure is adjusted to the anode gas pressure, the membrane valve of the implementation closes again, so that no air supply takes place on the cathode side. Suitable values for the pressure differences (Δp) are in the range of 1 to 1000 mbar, preferably 5 to 500 mbar. Suitable pulse times for one pulsating operation are 1 second to three hours, preferably 10 seconds to 180 seconds. In discontinuous operation, the cell for the regeneration of the anode catalyst can also be operated longer, ie up to a certain endpoint. These flexible operating options are of great importance for various applications.

combinations The above various embodiments are possible. The bushings can in principle be installed in both the active and non-active area and be provided with or without lining. You can continue be made with or without borders or recesses. Of others can diaphragm valves or other devices for controlling the Air or oxygen flow include.

The ion-conducting membrane generally contains proton-conducting polymer materials. Preference is given to using perfluorinated polymeric sulfonic acid compounds, for example a tetrafluoroethylene-fluoro-vinyl ether copolymer having sulfonic acid groups. This material is sold under the trade name Nafion ^® by DuPont. However, other, in particular fluorine-free ionomer materials, such as doped sulfonated polyether ketones or doped sulfonated or sulfonated aryl ketones, polysulfones and doped polybenzimidazoles or ion-conducting ceramic materials can also be used.

The Gas distribution substrates on the anode and cathode side can be out porous electrically conductive Materials such as carbon fiber paper, carbon fiber fleece, carbon fiber fabric, Metal nets, metallized fiber fabrics and the like exist.

When Protective films or sealing materials can be used organic polymers be under the working conditions of the PEM fuel cell are inert and no disturbing Secrete substances. Suitable materials are thermoplastic Polymers such as polyethylene, polypropylene, PTFE, PVDF, Polyamide, polyimide, polyurethane or polyester; for another thermosetting polymers such as epoxy resins or cyanoacrylates. Also suitable are elastomers, such as, for example, silicone rubber, EPDM, fluoroelastomers, perfluoroelastomers, chloroprene elastomers, Fluorosilicone elastomers.

Of the Oxygen transported through the internal air flow to the anode takes care of a reduction of the anodic overvoltage, as they are e.g. by various impurities (e.g., CO in the reformate or CO as a residue in commercial hydrogen) in the anode gas in the PEM fuel cell becomes. You get a significant improvement in the performance of the PEMFC, without expensive To use gas cleaning equipment or control devices. The Fuel cell system is thus considerably simplified and ultimately cheaper.

The "internal air bleed " also for the oxidation or for the removal of further, the overpotential the anode negatively affecting impurities are used. Examples are additives, sulfur compounds or odorants, the on the catalyst surface adsorbed.

applications for the inventive technology are direct methanol fuel cells (DMFC), micro-portable fuel cells and fuel cell systems for the stationary Area. About that In addition, the technology can also be used for mobile applications which are mostly operated on a hydrogen basis, the Hydrogen depending of its purity (e.g., 3N or 5N), a residual concentration CO may contain up to 50 ppm.

The Production of the membrane-electrode unit according to the invention can with all common Methods, for example by the CCM, CCB or decal method respectively. In the CCM process, the catalyst-coated membrane (CCM) with bushings Mistake. However, it can also be the membrane electrode assembly with sealing edge or protective film or the ionomer membrane itself with one or more bushings be provided. You can do this commercial Perforation tools (mandrels, hole punches, needles, hole pliers or similar) be used. The perforation process can be continuous MEE manufacturing process to be integrated.

The Lining of the bushings can by means of tubes, sleeves, Hollow rivets, but also by punching or by applying adhesive done. Should the bushings be provided with a valve, this can manually or mechanically on or in execution be positioned and additionally, if necessary with adhesive, be attached. The necessary manufacturing steps are known in the art.

The The following examples illustrate the invention.

EXAMPLE 1

MEE with implementation, continuous Operation with "internal air bleed ":

By means of known methods (cf., for example EP 1 037 295 B1 A catalyst-coated membrane ("CCM") with 25 cm ² (5 x 5 cm) active catalyst area is prepared, the catalyst loading being 0.4 mg / cm ² PtRu on the anode and 0.4 mg / cm ² Pt on the anode The ionomer membrane is a perfluorinated polymer electrolyte membrane with a thickness of 25 microns, in the edge region of the CCM on both sides circumferentially a polyurethane protective film with a width of 1 cm and a thickness of 50 microns is appropriate.In this edge region is using a mandrel introduced a passage with an inner diameter of d = 1 mm.

Subsequently the CCM is provided with gas distribution substrates on the anode side and cathode side and installed in a single PEM cell with bipolar plates. The gas supply channels of the bipolar plates are aligned on the anode side and cathode side so that This implementation against the Inlet channel of the reformate gas at the beginning of the anode flowfield as well across from the inlet channel of the air is located at the beginning of the cathode flowfield. This allows a continuous internal air transport.

The PEM single cell is measured in a standard fuel cell booth that has an electronic load. The measurements are made using synthetic reformate with a gas composition of 75% H ₂ , 25% CO ₂ , and 300 ppm CO on the anode side and air on the cathode side. The gases are set on the anode side with a conversion of 30% and on the cathode with a conversion of 20%. Due to the different geometries of the flowfields and the selected gas quantities, a pressure difference occurs between the cathode and anode sides. The pressure difference (Δp) is 10 mbar. The cell temperature is 40 ° C. At a constant voltage of 670 mV, a current density of about 200 mA / cm ^{2 is obtained} . This achieves an average power density of approx. 120-140 mW / cm ² . This high performance can be maintained in the endurance test over a period of more than 200 h (cf. 5 , upper curve).

COMPARATIVE EXAMPLE 1

MEE without execution, continuous Operation without "internal air bleed ":

A 25 cm ² (5 x 5 cm) catalyst-coated membrane (CCM) is prepared as described in Example 1, but no feedthrough is performed so that no "internal air bleed" occurs.

The CCM comes with gas distribution substrates on anode side and cathode side fitted into a single PEM cell and in a standard fuel cell test stand measured. The measurement conditions are identical to those in Example 1 . described

At a cell voltage of 670 mV gives a current density of about 50 mA / cm ² , which corresponds to a typical power density of 35 mW / cm ² . This value is about 100 mW / cm ² below the value of Inventive Example 1 (cf. 5 Lower curve "Standard R300") The advantageous effect of the membrane-electrode unit according to the invention with bushing is thus confirmed.

EXAMPLE 2

MEE with bushing, pulsating Operation with "internal air bleed ":

A catalyst coated membrane ("CCM") with 25 cm ² (5 x 5 cm) active catalyst area is prepared as described in Example 1. The catalyst loading is 0.4 mg / cm ² PtRu on the anode and 0.4 mg / cm ² Pt on the cathode The ionomer membrane is a perfluorinated polymer electrolyte membrane with a thickness of 25 microns, in the edge region of the CCM is on both sides circumferentially a polyurethane protective film with a width of 1 cm and a thickness of 50 microns a passage with an internal diameter of d = 1 mm is introduced with the aid of a mandrel For the pulsating operation with "internal air bleed", the passage on the anode side is provided with a diaphragm valve.

Subsequently the CCM is combined with gas distribution substrates on anode side and cathode side and, as described in Example 1, in a single PEM cell with Bipolar plates installed.

The PEM fuel cell is first operated at normal pressure (p = 1 bar) with synthetic gas mixture reformate 75% H ₂ , 25% CO ₂ , and 300 ppm CO on the anode side, air is used on the cathode side. The cell temperature is constantly 40 ° C. After due to the CO poisoning of the anode catalyst, the cell voltage has dropped to less than 200 mV, the cathode pressure is increased by means of the pressure regulator by 50 mbar (pressure difference Δ p = 50 mbar). As a result, a controlled air flow reaches the anode side, the anode catalyst is thereby regenerated. In Within 1 minute, the cell voltage rises again to the initial value. Thereafter, the cathode pressure is regulated back to 1 bar. This process can be repeated any number of times, with pulse times of 1 second to three hours are possible.

Claims (29)

Membrane electrode unit for electrochemical devices, containing an ionomer membrane with front and rear side, at least one gas diffusion substrate, at least one protective film and at least one catalyst layer, wherein the ionomer membrane has at least one passage, which has an internal Air transport from the cathode side to the anode side allows. A membrane-electrode assembly according to claim 1, wherein the at least one implementation is mounted in the region of a catalyst layer. Membrane-electrode assembly according to claim 1 or 2, the at least one implementation is mounted in the region of the at least one protective film. Membrane-electrode assembly according to one of claims 1 to 3, wherein the at least one passage has an inner diameter (d) in the range of 5 to 5000 microns having. Membrane-electrode assembly according to one of claims 1 to 4, where the number of feedthroughs between 1 and 10, preferably between 1 and 5. Membrane-electrode assembly according to one of claims 1 to 5, wherein the at least one protective film thermoplastic polymers from the group of polyethylenes, polypropylenes, polytetrafluoroethylenes, PVDF, polyesters, polyamides, polyamide elastomers, polyimides and polyurethanes and / or elastomers from the group of silicones, silicone elastomers, EPDM, fluoroelastomers, perfluoroelastomers, chloroprene elastomers, fluorosilicone elastomers and / or thermosetting polymers from the group of epoxy resins, phenolic resins and cyanoacrylates. Membrane-electrode assembly according to one of claims 1 to 6, wherein the at least one bushing has a lining. A membrane-electrode assembly according to claim 7, wherein lining thermoplastic polymers from the group of polyethylenes, Polypropylenes, polytetrafluoroethylenes, PVDF, polyesters, polyamides, polyamide elastomers, Polyimides and polyurethanes and / or elastomers from the group of Silicones, silicone elastomers, EPDM, fluoroelastomers, perfluoroelastomers, Chloroprene elastomers Fluorosilicone elastomers and / or thermoset polymers from the Group of epoxy resins, phenolic resins and cyanoacrylates has. A membrane-electrode assembly according to claim 7, wherein the lining comprises metals or ceramic materials. A membrane-electrode assembly according to claim 7, wherein the lining of the material of the at least one protective film consists. Membrane-electrode assembly according to one of claims 1 to 10, wherein the at least one implementation provided with a border is. A membrane-electrode assembly according to claim 11, wherein the border thermoplastic polymers from the group of polyethylenes, Polypropylenes, polytetrafluoroethylenes, PVDF, polyesters, polyamides, polyamide elastomers, Polyimides and polyurethanes and / or elastomers from the group of Silicones, silicone elastomers, EPDM, fluoroelastomers, perfluoroelastomers, Chloroprene elastomers Fluorosilicone elastomers and / or thermoset polymers from the Group of epoxy resins, phenolic resins and cyanoacrylates has. Membrane-electrode assembly according to one of claims 1 to 12, wherein the border of the material of the at least one protective film consists. Membrane-electrode assembly according to one of claims 1 to 13, wherein the at least one implementation with a device for controlling the air transport, preferably provided with a valve is. A membrane-electrode assembly according to claim 14, wherein the at least one implementation having a diaphragm valve. Membrane-electrode assembly according to one of claims 1 to 15, wherein the ionomer membrane organic polymers, such as proton-conducting perfluorinated polymeric sulfonic acid compounds, doped sulfonated Polyether ketones, doped sulfonated or sulfinated aryl ketones, Polysulfones, doped polybenzimidazoles or ion-conductive ceramic Has materials. Membrane-electrode assembly according to one of claims 1 to 16, wherein the at least one gas distribution substrate porous, electrically conductive Materials such as carbon fiber paper, carbon fiber fleece, carbon fiber fabric, Metal nets, metallized fiber fabric, etc. has. Membrane-electrode assembly according to one of claims 1 to 17, wherein the at least one catalyst layer noble metal-containing Contains catalysts. Membrane fuel cell containing a membrane-electrode assembly according to one the claims 1 to 18. Method for operating a membrane fuel cell with contaminated hydrogen, with an internal air transport from the cathode to the anode. The method of claim 20, wherein the membrane fuel cell a membrane-electrode unit according to one of the claims 1 to 18. The method of claim 20 or 21, wherein the internal Air transport from the cathode to the anode takes place continuously. Method according to one of claims 20 to 22, wherein the internal Air transport from the cathode to the anode by a pressure difference (Δ p) is controlled. Method according to one of claims 20 to 23, wherein the pressure difference Δ p> 0. Method according to one of claims 20 to 24, wherein the pressure difference (Δp) in Range of 1 to 1000 mbar, preferably in the range of 5 to 500 mbar is located. Method according to one of claims 20 to 25, wherein the pressure difference (Δp) in Pulse times from 1 second to three hours, preferably 10 seconds up to 180 seconds. Membrane fuel cell stack containing the membrane-electrode assembly according to one the claims 1 to 18. Use of the membrane-electrode assembly after one the claims 1 to 18 in electrochemical devices, in particular membrane fuel cells. Use of the membrane-electrode assembly after one the claims 1 to 18 in direct methanol fuel cells (DMFC).