WO2016162289A1

WO2016162289A1 - Membrane electrode unit with an electrically conductive element

Info

Publication number: WO2016162289A1
Application number: PCT/EP2016/057295
Authority: WO
Inventors: Manuel Schneiter
Original assignee: Volkswagen Ag
Priority date: 2015-04-10
Filing date: 2016-04-04
Publication date: 2016-10-13
Also published as: DE102015206423A1

Abstract

The invention relates to a membrane electrode unit (101) comprising a membrane (103), an anode (102) arranged on a first membrane side (106), and a cathode (104) arranged on a second membrane side (107), wherein, when viewing the flat sides thereof, the membrane electrode unit (101) has a reaction region (112), at least one exchange region (114) in which at least one inlet opening (1101) and at least one outlet opening (1141) are formed for introducing and discharging gas (1103) and cooling fluid (1102), and at least one redirection region (111, 13) arranged between the reaction region (112) and exchange region (114), wherein the membrane electrode unit (101) has at least one first sealing region (1171) enclosing the redirection region (111) and the reaction region (112) for sealing the membrane electrode unit against a bipolar plate. According to the invention, at least one element (1111) is provided which has an electrical conductivity, depending on at least one parameter, for short-circuiting the anode (102) using the cathode (104) and is arranged within the first sealing region (1171).

Description

description

Membrane electrode unit with an electrically conductive element

The invention relates to a membrane-electrode assembly comprising at least one

Exchange region, a forwarding region and a reaction region comprises, wherein at least one inlet opening and at least one outlet opening for introducing and discharging gas and coolant liquid are formed in the exchange region and the membrane electrode assembly at least one membrane and at least one cathode and at least one anode for catalyzing of the gas at the cathode or the anode, wherein the cathode is arranged on a first membrane side and the anode is arranged on a second membrane side

Membrane side is arranged and wherein the membrane-electrode unit comprises at least one sealing area.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as core component the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a composite of an ion-conducting, in particular proton-conducting membrane and in each case an electrode arranged on both sides of the membrane (anode and cathode). During operation of the fuel cell, the fuel, in particular hydrogen H ₂ or a

hydrogen-containing gas mixture is fed to the anode, where an electrochemical oxidation takes place with release of electrons (H ₂ -> 2 H ⁺ + 2 e ^" ). The membrane, which separates the reaction spaces gas-tight from each other and electrically isolated, takes place

(water-bound or anhydrous) transport of protons H + from the anode compartment into the cathode compartment. The electrons e ^" provided at the anode are fed to the cathode via an electrical line, and the cathode is supplied with oxygen or an oxygen-containing gas mixture, so that the oxygen is reduced by taking up the electrons (2 0 ₂ + 2 e -> 0 ^{2 ~} ). At the same time, these react in the cathode compartment

Oxygen anions with the protons transported across the membrane to form water (2 H ⁺ + O ^{2 "} -> H ₂ O).

In general, the fuel cell is formed by a plurality of stack (stack) arranged membrane electrode assemblies whose electrical power is added. Between two membrane-electrode units, a bipolar plate is arranged in each case in a fuel cell stack, on the one hand, the supply of the process gases to the anode or Cathode of the adjacent membrane electrode assemblies and on the other hand, the dissipation of heat is used.

Membrane electrode assemblies (MEA) are installed in fuel cells that drive vehicles. So they are exposed to the weather conditions that these

Suffer vehicles. Low temperatures below freezing freeze water and product water in fuel cells to ice. This ice clogs, among other things, the supply and discharge channels of the fuel cell operating gases. These blockages interfere with the gas supply and prevent a reliable cold start of the fuel cell stack. In addition, components are incorporated in a fuel cell stack

Materials that partially release substances. Their release results from a sensitivity of the components or materials for heat, moisture or hydrogen. These substances are a pollution or a

Pollution source for the MEA. A contaminated MEA suffers in its functionality or takes damage. Thus, contamination threatens the reliability of the

Fuel cell stack. Therefore, components and materials that are not necessarily part of the MEA are usually installed outside of a sealing ring. However, cooling outside the sealing ring is limited or not available. The sealing ring usually seals the MEA along its frame.

If ice clogs the flow channels of the anode and thus causes a lack of fuel at the anode, this can lead to the polarity reversal of individual cells of a fuel cell stack.

US 2010/0035090 A1 discloses in FIG. 2 that a nonlinear element is to be placed between two bipolar plates in order to reduce MEA degradation. The script proposes to use as a nonlinear element a PTC resistor or a MOSFET resistor. These are, according to paragraph [0023], to be integrated outside the bipolar plate in the fuel stack. Alternatively, the non-linear element is in others

Place fuel cell stack structures. The non-linear element can also be used as a component within a bipolar plate, a gas seal or electrical

Insulating device or as part of a conductive layer or other support structures are installed.

A disadvantage of the proposal of US2010 / 0035090 is the strong alternating load of the bipolar plate in the vicinity of the non-linear element, the regular heating and cooling of which loads the bipolar plates. The disadvantage is the complexity of Seals. Their suitability for use in fuel cells requires a high level of knowledge and skills. Producing suitable stamped or cut gaskets or seals from dispensers is complicated.

DE 10 2007 048 869 A1 teaches the use of a PTC element as one

Self-regulating resistor in connection with a fuel cell stack. The Script teaches in paragraph [001 1] to use this PTC element, one through the

Fuel cell to limit the voltage generated until the fuel cell has reached a normal operating temperature. To implement this task, the PTC element is installed between two bipolar plates. Because there it closes both bipolar plates together electrically short, as long as the switching resistance of the PTC element is not reached. Scripture teaches to integrate a PTC element, for example, into each bipolar plate or membrane therebetween.

The disadvantage, however, is that the PTC element is clamped with leaf springs between the bipolar plates. A jamming of components is uncertain. A second disadvantage is that the preferred location for the PTC element is to be near the coolant inlet manifold. However, since this location has no contact with the coolant, the thermal coupling is low.

Starting from DE 10 2007 048 869 A1, the prior art has the disadvantage that heating or heating of a bipolar plate arrangement or the fuel cell stack takes too long when cold starting a vehicle. To overcome this drawback, attempts have been made to flush fuel cells with dry air. Neither the rinsing nor the heating of valves or coolant solved this disadvantage. Even a skilful, ice tolerant, constructing the MEA created no remedy. Due to the great desire of the art to remedy the disadvantage, it was tried to exploit a combustion of H ₂ and 0 ₂ . The delay in the cold start of vehicles continues.

The invention is based on the object of further improving the heating of a fuel cell stack during its cold start.

This object is achieved by a membrane-electrode assembly and by a

Fuel cell stack solved with the features of the independent claims.

The membrane-electrode unit according to the invention comprises a membrane, a cathode arranged on a first membrane side and a membrane side on a second side arranged anode. The membrane electrode assembly has in plan view on its flat sides in each case a reaction region, at least one exchange region in which at least one inlet opening and at least one outlet opening for introducing and discharging gas (anode and cathode operating media) and coolant liquid are formed, and at least one arranged between reaction area and exchange area

Forwarding area. Furthermore, the membrane-electrode unit has at least one first sealing region enclosing the at least one forwarding region and the reaction region for sealing the membrane-electrode assembly against a bipolar plate (in the assembled state in a fuel cell stack). The object is achieved in that at least one element is present which has an electrical conductivity dependent on at least one parameter for short-circuiting the cathode to the anode and which is arranged within the first sealing region.

The invention in a further aspect relates to a fuel cell stack comprising a plurality of alternately arranged membrane-electrode assemblies according to the invention and bipolar plates. The fuel cell stack can be advantageously used in an electric motor-operated vehicle, wherein the fuel cell stack supplies the electrical energy for operating the electric motor.

The reaction region (also referred to as the active region) is an area where the catalytic electrodes are present. In the assembled state in a fuel cell stack, the reaction area of the membrane-electrode unit adjoins in each case an adjacent bipolar plate which has an open flow field in this area, for example open flow channels through which the reactant gases, ie the anode or cathode operating gas, flow. In the reaction area, the chemical fuel cell reactions thus take place during operation of the fuel cell. In the interior of the bipolar plate flow channels are present in the reaction region through which the coolant flows and dissipates the heat of reaction. The exchange area is an area in which the openings for the supply and removal of the operating media, ie the anode and

Cathode operating medium and the coolant are present. Preferably, the membrane-electrode unit has two exchange areas, in each of which three openings (one for each operating medium) are formed and which are arranged opposite each other on both sides of the reaction area. In the fuel cell stack, these openings are arranged congruently with corresponding openings of the bipolar plates, whereby main media channels are formed, which pass through the stack in the stacking direction. On the side of a bipolar plate adjacent to the membrane-electrode unit are in the exchange area usually no flow channels for the reactants and the coolant present. The relay area (also called distributor area) denotes an area which is arranged between the reaction area and an exchange area. The forwarding area serves the fluid connection between the openings of the exchange area, so the

Main media channels, and the inner and outer channel structures of the reaction area. For this purpose, inner and outer flow channels are present on a bipolar plate adjacent in the assembled state, which connect the corresponding outlet openings of the exchange area with the corresponding inner and outer flow channels of the bipolar plate of the reaction area. Since no chemical reactions are to take place in the forwarding area as well as in the exchange area, the membrane-electrode unit has no electrodes in these areas

Electrode coating on. In contrast to the active reaction area of the

Exchange area and forwarding area together also referred to as inactive area. The terms reaction region, exchange region and transfer region refer to the plan view of one of the two flat sides of the membrane-electrode assembly, these regions being formed on both flat sides.

In that, according to the invention, each membrane-electrode unit passes through the element

(hereinafter also referred to as a short-circuit element) can be internally short-circuited depending on the at least one parameter, the membrane-electrode unit loses its resistance and is traversed by electrical currents, wherein heat is dissipated. The current flow is independent of the electrical resistances of other fuel cell stack structures. It heats all operating media in the

Fuel cell stack in the vicinity of the installation of the short-circuit element to flow through the adjacent bipolar plate. Since the short-circuit element is arranged in the sealing region of the membrane electrode assembly, that is, in a relay region and / or

Reaction area, the element is in close proximity to a cooled area of an adjacent bipolar plate, that is, at least one inner coolant channel thereof. Thus, by the heat emission of the short-circuit element in particular to a heating of the coolant, which in turn distributes the heat through the bipolar plate. If, after switching off the fuel cell stack in the anode or

Cathode channels of the bipolar plate has formed frozen product water, which leads to the blockage of these channels, so this ice is thawed quickly by the short-circuit element and the channels are free. Therefore, the fuel cell according to the invention produces faster power during cold start. This makes the fuel cell stack more effective and requires fewer cells or membrane-electrode assemblies. The advantage of this Efficiency gain is a saving of cells and thus of space. Because the

According to the invention membrane electrode assembly is heated by the short-circuit element, the coolant when starting the fuel cell stack must be heated less than in the prior art, whereby a coolant heater is possibly unnecessary. Other measures of heating can also be reduced, thereby reducing weight and costs. Another advantage is that each membrane-electrode assembly and thus each adjacent bipolar plate is heated separately. The entire fuel cell stack heats up quickly, even if individual cells fail because flow channels of adjacent bipolar plates are blocked by ice. The fuel cell stack consequently heats up reliably. A current drain from the fuel cell stack can thus take place as soon as a single cell is free of ice blocks, especially once a

Minimum number of single cells is ready.

Another advantage of the internal short circuit of the cells is the fact that they do not reverse polarity over their intended polarity, since electrical charges are dissipated and compensated via the element. Since reversals that can take place after a shutdown of the fuel cell stack, at the start of damaging effect on the catalytic material of the anode and in particular the cathode, by the membrane electrode unit according to the invention, the creeping reduction of

Reduced efficiency of the fuel cell with the useful life.

Another advantage is that the membrane-electrode assembly according to the invention is robust to short-distance use. If some cells are not yet ice-free, they will not operate during short-distance use. You will be spared, but one

Fuel cell stack is still operational by the other, ice-free cells.

The conductivity of the short-circuit element depends on at least one parameter. A meaningful parameter reflects the weather or its changes, in particular the

Presence of frost conditions.

The short-circuit element is preferably designed so that it has a low or no electrical conductivity under operating conditions of the fuel cell stack and thus there is no short circuit. However, outside the operating conditions of the fuel cell stack, the element has a high electrical conductivity and short circuits the anode and cathode. Preferably, this conductivity behavior of the element is passive in response to the parameter. The parameter is in a specific embodiment a control signal provided by an electronic unit. The electronic unit measures the environment of the fuel cell on the basis of different parameters. Then it can reproduce a control signal from the different measured variables. In the operation of vehicles these are

Environmental conditions Position coordinates of a GPS system, a salary

Antifreeze in windscreen wiper water, stored data of a driving history,

Temperatures, pressures or historical data on the number of operating hours

Fuel cell.

In an advantageous embodiment, the parameter is a temperature, a

Gas concentration or a voltage. If the parameter is a temperature, the element is preferably designed such that its conductivity changes greatly in the region of the freezing point of water, ie in the range around 0 ° C. (+/- 20 ° C., in particular +/- 15 ° C.) , If the temperature is below freezing or below a safe limit above freezing, the cell will be shorted and thus heated. The parameter can also be a gas concentration. The advantage is the dependence of the conductivity of the life of a vehicle, because the gas concentration, for example of hydrogen, can be greatly reduced if the vehicle has stood for a long time. Alternatively, the parameter is a voltage. In this case, the membrane-electrode unit is short-circuited until reaching a predetermined threshold voltage. It has no polarity and can not reverse polarity. To interconnect the cathode with the anode via a diode is a possibility in this context, because it prevents an electric current in an undesired direction within its blocking region. This protects against a polarity reversal.

In a preferred embodiment, the element is a PTC element. The advantage is a short circuit of the MEA as a function of the temperature without expensive and expensive electronics. Each PTC element passively switches its associated MEA depending on the conditions prevailing at its position in the fuel cell stack. A shunt of a PTC element within the MEA allows its shunting without electrical resistances flow through other fuel cell structures.

Alternatively, the cathode and the anode may be bonded together by a foil having an oxide layer. This has the advantage that a hydrogen injection into the

Cathode supply can be injected to react at the anode during startup to the Short circuit MEA. Because then the oxide layer internally shorts the MEA short. This keeps the anode free of any harmful effects.

In another embodiment, the element is a diode. A diode, such as a reverse polarity protection diode, directs the current between the shorted cathode and anode in one direction. A use of a

Temperature-dependent reverse polarity protection diode allows operation of a

Diodes heater.

In a further embodiment, the element is a field effect transistor. A metal oxide semiconductor field effect transistor (MOSFET) has the advantage of being the least possible resistance in the case of a short circuit. At the same time, it offers the best possible protection against reverse polarity. A MOSFET also allows to integrate other circuit components. The advantage of this integration is voltage and temperature dependencies

Install circuit components in the MEA.

Advantageously, the element is arranged in the forwarding region of the membrane-electrode assembly. The forwarding area has sufficient installation space to insert thin and large-area short-circuiting means into the membrane-electrode unit. If one of two existing forwarding areas is a media supplying area and the other is a discharging area, the shorting element is preferably in the feeding one

Forwarding area positioned. In this way, the coolant is heated before it flows to the reaction area. The positioning of the element in the media-discharging forwarding area of the outlets, on the other hand, allows heating of the coolant as it exits the MEA. Since in the fuel cell reaction product water is formed, which is discharged from the reaction area via the laxative forwarding area with the exhaust gas, the risk of freezing of product water in the medienabführenden

Forwarding area particularly high. The advantage of heating at the outlet minimizes the risk of frost so sustainably at the place of the highest risk. Advantageously, one or more short-circuit elements may be provided both in the forwarding and in the discharging forwarding area.

In a further preferred embodiment, the element is within the

Reaction area arranged. The reaction area generally has a larger area than the relay area and a less strongly crossing channel structure on the part of an adjacent bipolar plate. He therefore has simpler flow conditions. A Heat transfer from the reaction region to the coolant flowing in the adjacent bipolar plate may be more directly possible in many plate designs than out of the relay region. An arrangement of two or more elements in the area of the

Forwarding range and the reaction area is advantageous because the heat-up effects of multiple elements add up, so that a fuel cell vehicle is ready for cold start very quickly.

In order to be able to short-circuit the anode to the cathode of the membrane-electrode assembly, the short-circuit element is designed to penetrate the membrane, that is to say that it is arranged in an opening in the membrane. In a further embodiment, the element is integrally inserted into the membrane-electrode unit. Integrally, the element is connected to the MEA, for example, if it is materially connected to this. But also an insertion of the element into the MEA connects the two components to form a component.

In a further embodiment, at least one second short-circuit element is present, which is a diode. Particularly preferred is the combination of a diode with a PTC element. Characterized in that at least one diode and at least one PTC element are arranged in the membrane-electrode unit, the sensitivity of the MEA can be adapted to the weather even better, because the diode may be positioned in the feeding forwarding area, so near the inlet openings, the PTC element, however, in the dissipative forwarding area near the outlet openings. Thus, both the supplied gas from the diode and the discharged gas from the PTC element is heated. An advantage of this separate dual heating is the ability to configure different switching temperatures of the diode and the PTC element. The diode and PTC elements can be designed for different switching temperatures. Thus, incoming gas or coolant may be heated at a different temperature than gas or coolant to be discharged. The advantage is the saving of energy, because gas to be discharged has a higher heat during operation than gas to be admitted and therefore has to be heated less.

In a further preferred embodiment, at least one second short-circuit element is present in the membrane-electrode unit, which is a field-effect transistor, preferably in addition to a diode. Also advantageous is the arrangement of a second short-circuit element in the form of a PTC element, in particular in combination with a field effect transistor. In a further embodiment, the membrane-electrode unit has at least one edge reinforcement, which has at least one element. The edge reinforcement is usually arranged in the non-active region of membrane-electrode assemblies, ie the exchange region and the forwarding region. It has a stabilizing function for the fragile membrane and is designed, for example, as a plastic film which supports the membrane in its electrode-free areas. The edge reinforcement can be used for the installation of the element in an advantageous manner, since the membrane is particularly well stabilized here. In one embodiment, the element is embedded between two metal plates in the edge reinforcing material. As a result, the element is housed in metal plates and sealed against the environment. In order to clamp the element between the metal plates, it can be held between the metal plates by a conductive pressure layer or a pressure element, such as a compression spring. The element jams particularly well when the gaps between the two metal plates are glued circumferentially with sealant.

In a further embodiment, the element is sealed separately by a second seal. Thus, the element is in the forwarding area separately against a

Bipolar plate half sealed. The separate seal increases the operational safety, because the seal redundancy is increased.

In a further embodiment, the element is formed integrally within a sealant. This has the advantage that the element is isolated from the operating gases. Consequently, it is not attacked by them. Also, pouring the element into a sealant, for example, the edge reinforcement, manufacturing technology is easy.

In a further embodiment, the element and the membrane-electrode assembly are made in one piece. One-piece components can easily be installed further and are less susceptible.

Another advantage of the invention is the fact that the operating state and thus a readiness for operation of the fuel cell stack according to the invention can be read from its voltage. A corresponding method is explained below with reference to the example of a PTC element as a short-circuit element.

The open circuit voltage can also be referred to as a so-called open circuit (OCV: Open Circuit Voltage). The open circuit voltage is the maximum voltage of a Fuel cell. It occurs when the fuel cell has reached its operating temperature and no load is applied. The existence of an operating temperature can thus be over the

Detect fuel cell when its maximum voltage is reached.

The approach to determining operational readiness lies in the relationship between

Temperature and resistance as the principle of action.

To recognize the operational readiness current-voltage characteristics of the

Provided fuel cell stack and the short-circuit element and deposited for example in a control unit of the fuel cell stack.

Current-voltage characteristics of the fuel cell stack form the non-linear

Relationship between current and voltage of a cell in each case for a constant anode and cathode gas supply (constant cell pressures or mass flows of the operating media) and a constant temperature. It increases with increasing

Amperage the voltage. The highest cell voltages are at current levels near zero. On the other hand, the characteristic shifts with increasing cell pressures or mass flows of the operating media in the direction of higher voltages and currents. A similar shift of the characteristics of the fuel cell is dependent on the

Temperature before.

The current-voltage characteristic of the short-circuit element, for example, a PTC element, however, usually has a linear course, in which the voltage

increases proportionally with the current and the slope of the line corresponds to the resistance of the element. The element changes its resistance depending on

Temperature. Thus, the element has a current-voltage characteristic for each temperature, the slope increasing with higher temperatures. In other words, the characteristic "wanders" with increasing temperature in the direction of higher voltages.

The voltage and the current through the membrane-electrode assembly are known, since they have corresponding current or voltage measuring devices in

Fuel cell systems are constantly recorded. They are also attached to the element. Of the

Resistance of the element can be calculated from this knowledge, so that a temperature can be assigned to it by its stored characteristic curve. The fuel cell is recognized as ready for operation, for example, when a temperature greater than 0 ° C is exceeded, because then the cell is free of ice. A preferred embodiment for carrying out this method comprises at least one fuel cell with at least one element, wherein the electrical resistance of the element is temperature-dependent. The method comprises the following steps:

Providing at least one current-voltage characteristic of a single cell of the

Fuel cell stack, wherein the characteristic represents the relationship between voltage U and current I of the cell. Alternatively, a plurality of current-voltage characteristics are provided, each characteristic indicating the relationship between voltage U and current I of the cell for different mass flows or operating pressures of the anode and / or cathode operating media,

• Determining the voltage U of the single cell or the fuel cell stack, from which the voltage U of each individual cell of the stack can be determined.

Determining the resistance R of the short-circuit element as a function of the

determined voltage U.

• Determining the temperature T of the single cell as a function of the determined

Resistor R of the shorting element.

• Determine the operational readiness when the temperature is a predetermined

Temperature threshold reached or exceeded, preferably from 0 ° C.

From this method results the advantage that there is a direct feedback whether a fuel cell is blocked by ice. This feedback also applies to the

Fuel cell stack. Further measuring means, such as temperature sensors are not necessary.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other. The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

FIG. 1 shows a sectional drawing of a fuel cell cut,

FIG. 2 shows a membrane-electrode unit in a plan view,

FIG. 3 an enlargement of a sectional drawing,

FIG. 4 is a perspective view of an MEA;

FIG. 5 shows a fuel cell stack with a cutout,

FIG. 6 shows a schematic representation of combinations of elements,

Figure 7 is a sectional view through a fuel cell cutout.

Figure 1 shows the schematic structure of a section of a fuel cell stack with two exemplary individual cells in a sectional view.

Each single cell has a membrane-electrode assembly (MEA) 101. The MEA 101 consists of a membrane 103 which has an anode layer 102 on its first membrane side 106 and a cathode layer 104 on its second membrane side 107. The anode or cathode layers 102, 104 can be applied directly to the membrane sides 106, 107 and cured. In this case, the MEA is also referred to as catalytically coated membrane or CCM (Catalyst Coated Membrane).

The CCM 105 is on both sides of an electrically conductive and gas-permeable

Gas diffusion layer 108, 109 contacted. The first gas diffusion layer 108 and also the second gas diffusion layer 109 are placed on the CCM 105 for this purpose. The

Gas diffusion layers 108, 109 adjoin bipolar plate halves 202.

Two bipolar plate halves 202 form a bipolar plate 201. Cathodic gas channels 203 for conducting cathode operating gas and anode gas channels 204 for conducting anode operating gas are present in the bipolar plate halves. The bipolar plate halves 202 also have cooling channels 205. These serve to cool the bipolar plates 201 from the inside. A plurality of alternately stacked bipolar plates 201 and membrane electrode assemblies 101 form a fuel stack 1 15.

FIG. 2 shows a membrane-electrode unit 101 in a plan view. The MEA 101 is stabilized by a frame-like edge reinforcement 1 16.

From left to right, the membrane-electrode unit 101 is subdivided into five regions, each of which is marked by a circumferential broken line in the figure: In a first exchange region 110, a first transfer region 11, a reaction region 112, a second forwarding area 1 13 and a second exchange area 1 14.

2 shows that in the first exchange area 1 10 individual inlet openings 1 101 are embedded. The inlet openings 1 101 are used for introducing coolant 1 102 and the anode and cathode operating gases 1 103. The inlet openings 1 101 are individually sealed, each with a circumferential seal (thick line) against an adjacent Bipolarplattenhälfte (not shown in Figure 2). In addition, the inlet openings 1 101 may be sealed with a seal surrounding the entire exchange area 110. The sealing of the inlet openings 101 1 individually and as an area increases the safety in the event of leakage.

Accordingly, the second exchange region 1 has 14 outlet openings 1 141 for draining the coolant 1 102 and the anode and cathode operating gases 1 103 and circumferential seals 11.

The first exchange area 110 thus represents the inlet side of the MEA 101 and is also referred to as inlet, while the second exchange area 14 forms the outlet side and is referred to as outlet.

The reaction region 1 12, which is also referred to as the active region, describes a region of an MEA 101, which lies between the first and second relay region 1 1 1, 1 13 and by the presence of the cathode and anode, ie the catalytic

Coating distinguishes. Thus, during operation of the fuel cell in the reaction region 12, the current-generating chemical reactions take place.

In the first relaying area 1 1 1, the anode operating gas 1 103, such as oxygen or air, and the cathode operating gas 1 103, for example, hydrogen or another Fuel, led from the inlet openings 1 101 to the catalytic electrodes of the reaction area 102 and distributed in this. In the second relaying area 1 13, the anode and cathode operating gas 1 103 are discharged from the reaction area 102 and the outlet openings 1 141 supplied. Likewise, the coolant 1 102 flows within an adjacent bipolar plate from the corresponding inlet opening 1 101 and is parallel to the first relay region 1 1 1, the reaction region 102, the second

Forwarding area 1 13 in the corresponding outlet opening 1 141 out. In the

Forwarding areas 1 1 1, 1 14 no chemical reaction of the reactants takes place.

Preferably, in the forwarding areas 1 1 1, 1 13 therefore no catalytic coating is present. However, the frame-like edge reinforcement 1 16 can extend advantageously over the forwarding areas 1 1 1, 1 13 extend. Forwarding areas 1 1 1, 1 13 are also referred to as plenum, manifold area, transition area, or cross-flow area.

The forwarding areas 1 1 1, 1 13 are referred to together with the exchange areas 1 10, 1 14 as so-called inactive areas.

The first and second forwarding areas 1 1 1, 1 14 are together with the

Reaction region 102 also sealed separately by a circumferential first seal 1 1 12 and form the here hexagonal sealing region 1 171 (in addition, indicated in Figure 2 by the hexagonal symbol). The first seal 1 1 12 is for example as

Solid rubber lip in a pre-lasered sealing groove of the edge reinforcement 1 16 inserted (not shown) or sprayed onto the edge reinforcement 1 16.

According to the invention, an element 1 1 1 1 is within the sealing region 1 171

(Short-circuit element), which is designed to produce an electrical short circuit between the anode 102 and the cathode 104 of the membrane-electrode assembly in dependence on a suitable parameter (see also FIG. 2). The short-circuit element 1 1 1 1 can be arranged in one or both forwarding areas 1 1 1, 1 13 and / or in the reaction area 102. At least in the case of the arrangement in a relay region 1 1 1, 1 13, where no anode or cathode coating is present, the electrical short circuit via the adjacent gas diffusion layers 108 and 109. The element may in various embodiments, a diode, a field effect transistor or a PTC Be element. Combinations of these are also beneficial.

In the example shown in Figure 2, the short-circuit element 1 1 1 1 is disposed within the first forwarding area 1 1 1 and there by an optional second seal 1 1 13th sealed separately. For this purpose it is surrounded by two metal plates which are sealed together along their edge, so that the element 1 1 1 1 is sealed between the metal plates. So that the element 1 1 1 1 is fixed between the metal plates, it is stretched with a spring between the metal plates. The element 1 1 1 1 breaks through the MEA 101 so that it connects the first gas diffusion layer to the second gas diffusion layer (not shown).

In a further embodiment, the element can also be installed several times. A

Possibility is the installation of an element on the inlet side and a second element on the outlet side. The second element may also be a diode, a field effect transistor or a PTC element. If necessary, the number of elements and the combinatorics of their versions as a diode, field effect transistor or PTC element can be changed.

In the present embodiment, the element 1 1 1 1 is cast in the first relay region 1 1 1. This is alternatively or additionally possible in the second forwarding area 1 13. The top and the bottom of the element 1 1 1 1 are applied to the first and second gas diffusion layer (not shown). Since the gas diffusion layers are electrically conductive, the element 1 1 1 1 can switch a short circuit between the cathode and the anode (not shown). This is done depending on a certain temperature, a certain external pressure, a certain voltage or a certain gas concentration of hydrogen or oxygen. The element 1 1 1 1 is designed so that it is not electrically conductive under normal operating conditions of the fuel cell.

In a further embodiment, the element 1 1 1 1 not directly through a

Operating parameters, but are switched by a control parameter of an electronic device. The setting parameter can be dependent on a variety of conditions. In vehicle construction, this is, for example, the position of the vehicle. Because this includes latitude and / or altitude above sea level. The electronic device also knows the history of different drivers, their driving behavior and their desired vehicle performance profile. For drivers who only set themselves up in the vehicle, the time between door opening and vehicle start, a slower heating of the element 1 1 1 1 can be set.

In order to achieve a high pressure stability, in a further embodiment, the first relay region 1 1 1 in parts, sub-segments or in the whole with its adjacent Bonded bipolar plate half or welded (not shown). Such joined seals withstand high temperatures or gas concentrations.

The reaction region 1 12 is subdivided into a membrane (not shown), as well as a cathode 102 or a cathode, which can be seen in plan view

Cathode coating 102. The cathode 102 is thus mounted on a first membrane side 106 (in the present view, the top of the membrane). On the other hand, the anode (not shown) is mounted on a second membrane side 107 (in the present view the underside of the membrane).

FIG. 3 shows an enlargement of a sectional view of a cell of a fuel cell stack 1 15. FIG. 3 teaches an MEA 301. An electrically conductive element 307 is arranged in the active region. The MEA 301 comprises a membrane 302, the one on both sides

Catalyst coating 303 has. This catalyst coating is in each case surrounded by a gas diffusion layer 304. The MEA 301 is sandwiched between two bipolar plate halves 305. The figure teaches that an element 306 is inserted in the MEA 301. The element 306 breaks through the membrane 302 and the catalyst coating 303. Thus, it is in electrical contact 306 with the catalyst coating 303. Also, there is electrical contact between element 306 and gas diffusion layer 304. Thus, if element 306 has no electrical resistance, then it short circuits MEA 101. Conversely, if it has a high electrical resistance, it isolates the

Catalyst coating 303 so that a potential arises between them.

The function of element 306 is shown in an enlarged replacement scheme. The replacement scheme shows the role of element 306. The task of element 306 is that of a potentiometer. This changes its conductivity 307 as a function of a

Parameters, such as the temperature.

The element 306 produces heat so that the MEA 301 heats up. The total heat of the MEA 301 is the sum of the electrochemical inefficiency. It adds to the heat radiated from the membrane-electrode assembly 301 and the heat of the member 306.

The element 306 is a PTC element in the present embodiment. Therefore, the total heat is directly proportional to the applied load on the membrane-electron unit 301 and the PTC element. A PTC element describes a device that having temperature-dependent properties. In particular, it describes

temperature-dependent electrical resistances. The abbreviation PTC stands for more positive

Temperature Coefficient. Other known names for PTC elements are PTC heating element or PTC shorting element. The switching temperature is the temperature at which a PTC element increases its resistance. A PTC element changes its resistance depending on its switching temperature. The switching temperature of a PTC element is in the operation of fuel cells for vehicles in the range of 50 to 70 ° C.

An MEA must be heated to have an open circuit voltage. A heated MEA, that is, an MEA whose coolant liquid has a temperature greater than 0 ° C, has the open circuit voltage when no consumer is connected. The

Open circuit voltage is also called OPC. The abbreviation OCV means Open Circuit Voltage. It describes an open circuit voltage. The open circuit voltage of a fuel cell is the

Voltage applied to a cell when no load is switched on. One cell describes an MEA along with the two associated gas diffusion layers and bipolar plate halves. If, according to an alternative embodiment, the element 306 is arranged in an inactive relay area (11 1, 13, 2), no catalyst coatings 303 are present in this area. In this case, the element 306 contacts the two gas diffusion layers 304 (not shown or 108, 109, Figure 1). The operation corresponds to the aforementioned.

FIG. 4 shows a perspective view of a membrane-electrode unit 401. The FIGURE shows an MEA 401 with two gas diffusion layers 401, 402. The MEA 401 is held by an edge reinforcement 404. FIG. 4 teaches different positions to place an element 403.

The element 403 may be placed inside the MEA 401 (right side of the illustration). For this purpose it is clamped in the membrane 408 between the cathode and the anode. Then it is automatically placed in the reaction area 406 as well. The element 401 is sealed separately (not shown)

In a further embodiment, the element 403 is arranged on one side of the membrane 408 in the transfer region 405, for example glued on. It does not break through the membrane itself. A bore (not shown) through the membrane 408 filled with an electrically conductive material performs this task. In another embodiment, placement of the element 403 within the edge enhancement 404 is also possible (left side of the illustration). That's it in

Forwarding area 405. The edge reinforcement serves primarily to mechanically support the membrane and is impermeable to the equipment. The edge reinforcement 404 may be a foil or a sheet that has openings as well as inlet and outlet openings (1 101, 1 141, FIG. 2). In some cases, edge reinforcement 404 is made in part or entirely of rubber or other non-electrically conductive material 407.

The element 403 may be a PTC element, a diode or field effect transistor in the present embodiment.

FIG. 5 teaches an embodiment of a fuel cell stack 501. Of the

Fuel cell stack 501 consists of bipolar plates 502 sandwiching MEA 504 between them. The embodiment teaches that the membrane 505 of the MEA 504 is pierced by an element 503. The element 505 is located in a relay area 506, wherein the element 505 is a switch 5031, a field effect transistor 5032, a diode 5033 or a

Resistor 5034 is. The field effect transistor is a MOSFET.

FIG. 6 shows different embodiments of the elements 601, such as switches, diodes, resistors and field-effect transistors. These are in the reaction area or in the

Forwarding area of the MEA combined. The inlet side, first forwarding area 1 1 1 in Figure 2, is characterized by an I (inlet), the outlet side, second forwarding area 1 14 in Figure 2, is marked with an O (outlet). Shown are different combinations of PTC element, diode, field effect transistor and open inlet opening or open outlet opening. From top to bottom, FIG. 6 shows the combination of a switch on the inlet side with a diode on the outlet side.

The diodes are thermal diodes. In the present embodiment is a thermal diode, which is known as a temperature sensor from the personal computer operation as a Schottky diode. These Schottky diodes are cheap to buy in large volume. Furthermore, they have positive properties according to US5955793. The diodes described here reach> 100mV / ° C in the working range of 5 ° C - 20 ° C. In this area, numerous diodes are used as temperature sensors.

In an alternative embodiment, a non-thermally responsive diode is installed. Such diodes are known to protect against cell reversal. In a second combination, there is a temperature sensitive resistor, a PTC element on the inlet side and a second PTC element on the outlet side. By means of this combination of two PTC elements, coolant liquids and gases in the inlet and outlet areas can be heated in different temperature ranges. Because the two PTC elements switch their resistance depending on their respective

Switching temperatures are different. This is explained in the diagram on the right in FIG. The PTC element on the side of the inlet has a switching temperature of -5 ° C to 5 ° C. The PTC element on the side of the outlet, however, has a switching temperature of 30 ° C.

In the illustrated embodiment, a PTC element is shown in ceramic design. Ceramic PTC elements are known in the automotive industry. They are used there for the defrosting of rear windows.

In another embodiment, the PTC element is a polymer design. It is a matrix of conductive particles, such as carbon, which finds support in a polymer. Such polymer designs are designed for high voltages.

In a third embodiment, there is a switch on the inlet side, while the outlet side is free of elements 601.

In the fourth case, the inlet side is free of elements 601, but on the outlet side is a PTC element.

FIG. 7 shows a detail of a fuel cell stack 701. Within the

Fuel cell stack 701 are two bipolar plate halves 702, 703. Between the bipolar plate halves 702, 703 is a membrane 706. This is connected by means of the two gas diffusion layers 704, 705 with the Bipolarplattenhälften. FIG. 7 also shows that the membrane 706 is separated from an element 709 by a film 707. The film 707 is cloth-impermeable. It also can not conduct electricity. Thus, it isolates element 709 from the MEA. Above and below the element, this is connected via deposits 708 to the gas diffusion layer 704, 705. The insert 708 is cloth-impermeable but electrically conductive. Thus, when the element 709, a PTC element or a diode or a MOSFET changes its resistance and a current flows, the MEA (not shown) is shorted. Suggestions for designations, special features and standards of seals are laid down in DIN 3750. Also in the Höischen, 29th edition p.31 1 the subject seals is briefly explained. There, for example, different types of seals, such as gaskets or gaskets are disclosed.

LIST OF REFERENCE NUMBERS

101 membrane electrode assembly

102 cathode (cathode layer)

103 membrane

104 anode (anode layer)

105 CCM

106 first membrane side

107 second membrane side

108 first gas diffusion layer

109 second gas diffusion layer

1 10 first exchange area

1 101 inlet opening

1 102 Coolant fluid

1 103 reactant gas

1 1 1 first forwarding area

1 1 1 1 element (short-circuit element)

1 1 12 first seal

1 1 13 second seal

1 12 reaction area

1 13 second forwarding area

1 14 second exchange area

1 141 outlet opening

1 15 fuel cell stacks

1 16 frames

1 17 seal

1 171 first sealing area

201 bipolar plate 202 bipolar plate half

203 cathode gas channels

204 anode gas channels

205 coolant channel

301 MEA

302 membrane

303 catalyst coating

304 gas diffusion layer

305 bipolar plate half

306 element

307 conductivity

401 MEA

402 gas diffusion view

403 element

404 edge reinforcement

405 forwarding area

406 reaction area

407 non-electrically conductive material

501 fuel cell stacks

502 bipolar plate half

503 element

5031 switch

5032 field effect transistor

5033 diode

5034 resistance

504 MEA

505 membrane

506 forwarding area

601 element

701 fuel cell stack

702 bipolar plate half

703 bipolar plate half Gas diffusion layer Gas diffusion layer Membrane

foil

inlay

element

Claims

claims

1 . A membrane-electrode assembly (101) comprising a membrane (103), an anode (102) disposed on a first membrane side (106), and an anode (102)

Diaphragm (104) arranged cathode (104), wherein the membrane-electrode unit (101) in plan view of their flat sides a reaction region (1 12), at least one exchange region (1 10, 1 14), in which at least one inlet opening (1 101) and at least one outlet opening (1 141) for introducing and discharging gas (1 103) and coolant liquid (1 102) are formed, and at least one between

Reaction region (1 12) and exchange region (1 10, 1 14) arranged

Forwarding region (1 1 1, 1 13), wherein the membrane-electrode assembly (101) at least one of the forwarding region (1 1 1) and the reaction region (1 12) enclosing the first sealing region (1 171) for sealing the membrane electrodes - Unit against a bipolar plate, characterized in that at least one element (1 1 1 1) is present, which has a dependent on at least one parameter electrical conductivity for shorting the anode (102) to the cathode (104) and within the first sealing region (1 171) is arranged.

2. membrane electrode assembly according to claim 1, characterized in that the

Parameter is a temperature, a gas concentration or a voltage.

3. membrane electrode assembly according to claim 1 or 2, characterized in that the element (1 1 1 1) is a PTC element.

4. membrane electrode assembly according to claim 1 or 2, characterized in that the element (1 1 1 1) is a diode.

5. membrane electrode assembly according to claim 1 or 2, characterized in that the element (1 1 1 1) is a field effect transistor.

6. membrane electrode assembly according to one of the preceding claims, characterized

characterized in that the element (1 1 1 1) within the forwarding area (1 1 1, 1 13) is arranged, in particular in a media-supplying forwarding area.

7. membrane electrode assembly according to any one of the preceding claims, characterized in that the element (1 1 1 1) within the reaction region (1 12) is arranged.

8. membrane electrode assembly according to one of the preceding claims, characterized

characterized in that at least one second element for shorting the

Anode (102) with the cathode (104) is present, which is a diode.

9. membrane electrode assembly according to one of the preceding claims, characterized

characterized in that at least one second element for shorting the

Anode (102) with the cathode (104) is present, which is a field effect transistor.

10. membrane electrode assembly according to one of the preceding claims, characterized

characterized in that at least one second element for shorting the

Anode (102) with the cathode (104) is present, which is a PTC element.

1 1. Membrane-electrode assembly according to one of the preceding claims, characterized

in that the membrane-electrode unit (401) has at least one

Edge reinforcement (404) and the edge reinforcement (404) at least one

Comprising element (403) for shorting the anode (102) to the cathode (104).

12. Membrane electrode unit according to one of the preceding claims, characterized

characterized in that the element (1 1 1 1) by a second seal (1 1 13) is sealed separately.

13. Membrane electrode unit according to one of the preceding claims, characterized

characterized in that the element (1 1 1 1) is integrally formed within a sealant.

14. Membrane electrode unit according to one of the preceding claims, characterized

characterized in that the element (709) in the membrane (706) is integrally formed.

15. A fuel cell stack comprising a plurality of alternately arranged membrane electrode assemblies (101) according to any one of claims 1 to 14 and

Bipolar plates (201).