WO2002011221A2

WO2002011221A2 - Device and method for wetting polymer electrolyte membrane fuel cells

Info

Publication number: WO2002011221A2
Application number: PCT/EP2001/008672
Authority: WO
Inventors: Andreas Schiegl
Original assignee: Proton Motor Fuel Cell Gmbh
Priority date: 2000-07-28
Filing date: 2001-07-26
Publication date: 2002-02-07
Also published as: AU2001282032A1; DE10036916B4; EP1412997A2; DE10036916A1; WO2002011221A3

Abstract

The invention relates to the wetting of polymer electrolyte membrane fuel cell stacks. At least one wetting water feed (12) is supplied with a plurality of first openings (15) in the fuel cell stack, these openings connecting the wetting water feed (12) to a reactant feed (10, 11). A plurality of second openings (17) are provided in the reactant feed (10, 11) connected to the wetting water feed (12), these second openings connecting the reactant feed to reactant distribution chambers (4, 6) of the individual fuel cells (2). The wetting water enters the reactant feed (10, 11) through the first openings (15) and is fed into the corresponding reactant distribution chambers by the reactant.

Description

Device and method for moistening polymer electrolyte membrane fuel cells

The invention relates to fuel cell stacks with a plurality of polymer electrolyte membrane individual fuel cells and with feeds for reactants and dampening water, each individual fuel cell having an anode, a cathode, an intermediate polymer electrolyte membrane and an anode-side and / or cathode-side reaction medium distribution space, and a method for moistening such fuel cell stacks. The fuel cells preferably use hydrogen or a methanol / water mixture in gaseous form as the fuel gas and air or as the oxidizing agent

Oxygen.

Polymer electrolyte membranes tend to dry out during the operation of the fuel cells, which initially leads to an increase in their internal electrical resistance and a decrease in the performance of the

Fuel cells and finally, if there is no humidification and the water balance of the cell is permanently disturbed, can lead to irreversible damage to the membrane. On the other hand, care must also be taken not to supply more than the required amount of dampening water to avoid flooding the electrodes. The maintenance and regulation of a water balance adapted to the respective operating conditions of the fuel cells is therefore one of the decisive operating criteria for polymer electrolyte membrane fuel cells.

Numerous attempts have been made to solve this problem. For example, it is known to use an external water evaporate and dampen the reaction gases with the gaseous water. Another alternative is to moisten the reaction gases in the fuel cell via a porous layer that is connected to the reaction gas spaces, the waste heat from the fuel cells possibly being used to evaporate the dampening water. Also known are fuel cell stacks with a separate moistening section, in which the reaction gases are moistened via a separating membrane using the waste heat from the fuel cell stack. Another attempt to solve this problem is described in German Patent No. 4318818. Here the reaction gases are humidified by injecting fine water droplets into the gas supply lines using air-assisted injection nozzles or ultrasonic atomizers before they enter the fuel cells. US Pat. No. 5,234,776, on the other hand, describes the humidification of the reaction gases by separately introducing fuel gas into the anode compartments and water into spaces above the anode compartments, from which it drips through openings in the anode compartments and runs in channels along the anode surfaces.

All known processes have the disadvantages that they require a great deal of additional construction work, have a high energy requirement, require special dampening water preconditioning and can only be adapted very inadequately to the dynamic load requirements of the fuel cells.

It is therefore an object of the present invention to provide an apparatus and a method with which the dampening water management of polymer electrolyte membrane fuel cells can be carried out easily and efficiently. can be achieved depending on the operating parameters.

Another object of the present invention is to provide a device and a method for moistening polymer electrolyte membrane.

To provide fuel cells that are simple in terms of equipment and undemanding.

It is also an object of the present invention to provide a device and a method for moistening polymer electrolyte membrane fuel cells with low energy requirements.

Another object of the present invention is to provide a device and a method for moistening polymer electrolyte membrane fuel cells in which areas with water

Undersupply and areas with excess water supply within the fuel cell stack can be avoided.

The object is achieved by a fuel cell stack with a plurality of polymer electrolyte membrane individual fuel cells and with

Feeds for reactants and dampening water, each individual fuel cell having an anode, a cathode, a polymer electrolyte membrane arranged therebetween and an anode-side and / or cathode-side reaction agent distribution space, characterized in that at least one dampening water feed is arranged to pass through the fuel cell stack and a plurality are arranged along its length has first openings, at least one reactant supply is arranged to pass through the fuel cell stack and has a plurality of second openings or interruptions along its length, wherein - the at least one dampening water supply is connected to the at least one reactant supply via the plurality of first openings, and wherein the at least one reactant supply via the plurality second openings or interruptions with the anode-side or cathode-side reactant distribution spaces of the individual fuel cells in connection.

The object is also achieved by the fuel cell humidification system, which has the aforementioned fuel cell stack, a humidification water reservoir, a humidification water pump and possibly a device for the pulsed supply of humidification water and a device for humidification water return.

The object is also achieved by a method for humidifying at least one reactant in a fuel cell stack with a plurality of polymer electrolyte membrane individual fuel cells and with feeds for reactant and dampening water, each individual fuel cell having an anode, a cathode, a polymer electrolyte membrane arranged in between, and an array-side and / - or has a reagent distribution space on the cathode side, characterized in that at least one dampening water supply is provided with a plurality of first openings via which the dampening water supply is connected to a reactant supply, a plurality of second openings or interruptions are provided in the reactant supply connected to the humidifying water guide, via which the reactant supply communicates with the anode-side or cathode-side reaction medium distribution spaces of the individual fuel cells, and dampening water is fed into the dampening water supply in liquid form, enters via the first openings into the reactant supply, is received by the reactant flowing in the reactant supply, and is fed together with the reactant into the anode-side or cathode-side reaction medium distribution spaces of the individual fuel cells.

The device and method according to the present invention can be used in fuel cell stacks with two or more fuel cells and also in individual fuel cells.

In the fuel cell humidification according to the invention, dampening water is fed in in liquid form via a dampening water supply which preferably supplies all individual fuel cells of the stack with dampening water. Alternatively, in particular in the case of large-area fuel cells, a plurality of dampening water feeds can also be provided, which jointly supply the individual fuel cells of a stack with dampening water or can be responsible for different individual fuel cells in a stack. If desired, certain individual fuel cells can be divided by several Humidification water supply, others, however, are only humidified by a humidification water supply. The invention is described below with the aid of a dampening water supply which supplies all individual fuel cells of a stack with dampening water centrally.

The dampening water supply leads liquid water directly into the fuel cell stack. It is connected to the fuel gas supply or the oxidant supply in such a way that the gas stream entering the stack entrains the dampening water emerging from the openings of the dampening water supply on its way into the individual fuel cells and distributes it finely and evenly in the anode-side or cathode-side reaction medium distribution space.

The entrainment of the dampening water through the reactant flow and metering into the individual fuel cells in the required amount is ensured by the inventive formation of the dampening water supply and the reactant supply (fuel gas and / or oxidizing agent). The dampening water supply duct, distributed over its length, has a plurality of first openings through which a reactant flows. For this purpose, the dampening water supply is arranged either inside the reactant supply or directly adjacent to the reactant supply. A connection of the dampening water supply and the reactant supply via connecting pieces which enable water to pass through is also possible in principle, but is less preferred because of the construction effort. Water is in the dampening water supply at a pressure which is slightly, ie preferably about 10 to 50 kPa, above the gas pressure on the anode or cathode side, so that the water can escape from the openings of the supply line. The cells are preferably operated at a pressure from atmospheric pressure to approximately 400 kPa, particularly preferably to approximately 200 kPa. The first openings of the moistening water supply are preferably selected so that the water emerges in the form of drops, the size of the openings being far more important than the shape of the openings. Round openings are generally chosen, in particular because of the simplicity of manufacture. The diameter of these water outlet openings is preferably 0.1 to 1.0 mm, particularly preferably 0.3 to 0.5 mm.

The humidification water is fed in continuously or, preferably, in pulses, i.e. only during the pulsation is the pressure in the

Humidification water supply high enough that water can escape from the first openings. In the case of pressure peaks, the pressure of 50 kPa given above can easily be exceeded. The pulse rate and pulse duration depend on the water requirement, ie on the operating state of the system, its dimensions and the design of the dampening water supply. A pulse rate of 1 pulse per 1 to 120 seconds and a pulse duration of 0.5 to 10 seconds are preferred. In particular, the infeed of the humidification water in pulses makes it possible to adapt the metered amount of humidification water exactly to the humidification water requirement. A pulse rate of 1 pulse per 10 to 40 seconds and a pulse duration of 0.8 to 2 seconds are particularly preferred. The dampening water is fed in by the pressure or, preferably, by a temporary pressure increase (pulses) in the dampening water supply. Aids that promote or cause the discharge of dampening water, for example piezo actuators or other means for generating sound waves or other waves, or a special nozzle-like configuration of the openings of the dampening water supply are not required. Only some type of dampening water delivery device, such as a pump, is therefore mandatory. In the case of pulsed feeding, a control valve is preferably also present.

As mentioned above, the dampening water supply is preferably arranged either within a reactant supply or directly on a reactant supply. The shape and cross-sectional area of the dampening water supply and the reactant supply are fundamentally arbitrary, as long as it is ensured that sufficient amounts of water and reactant can be supplied. Round and oval shapes are preferred.

The dampening water supply is arranged in or on the reactant supply in such a way that there are distances between the first openings and the second openings, which ensure that when the fuel cells are in operation, the dampening water emerging from the first openings is partly in the flow direction from the reactant flowing in the reactant supply is taken away.

In this preferred arrangement, the water emerging from the first openings is thus taken up by the flowing reactant and partly together with the reactant directly into the respective anode-side or cathode associated with the first openings. the reactant distribution spaces on the side, and in part carried along by the reactant in the reactant feed in the flow direction and fed into reactant distribution spaces located further downstream. This type of dampening water distribution is typically ensured when a substantial part, for example at least 30%, preferably at least 50%, of the reactant flows in the space between the first and the second openings, the form of the reactant supply also playing a role. The dampening water supply is particularly preferably arranged in or on one or the realdione agent supply (s) in such a way that the largest

Part of the volume of the reactant can be used for introducing the dampening water into the individual fuel cells.

If the dampening water supply is located within one (or the) reactant supply (s), it should therefore preferably not be arranged closer to the inlet openings of the reactant distribution spaces than is the case with an approximately coaxial arrangement, at least not over a longer area. An arrangement in the upper half of the reactant supply (s) is particularly advantageous, and very particularly preferably an arrangement on or near the upper edge of the reactant supply (s). In this way, the humidification water supply is flowed around completely or at least for the most part by the reactant, but the largest part of the reactant flows below the humidification water supply. If the dampening water supply and the reactant supply run parallel to one another and are only connected through the water outlet openings of the dampening water supply, the dampening water supply is also preferably arranged above the reactant supply. This ensures that for the entrainment, fragmentation, possibly atomization, and distribution of the water droplets emerging from the openings of the dampening water supply, all or at least the largest part of the reactant flow is available and, in addition, gravity can also be used for supply into each area of the reactant distribution rooms of each individual fuel cell. Depending on the temperature of the cells, a certain part of the dampening water changes to the vapor state after it has left the dampening water supply.

In order to achieve the precise metering of the amount of dampening water and in particular the rapid adaptation of the dampening water metering in accordance with the respective requirement profile, it is preferred to have the first openings in the dampening water supply, i.e. to provide the outlet openings of the dampening water for each individual fuel cell in the region of the entry into the reactant distribution space of the reactant transporting the dampening water. One or more water outlet openings can be provided for each individual fuel cell. As a rule, one water outlet opening per single fuel cell is completely sufficient. Several water outlet openings per individual fuel cell have the consequence that, with the same amount of water, the openings can be smaller, the emerging water drops are therefore also smaller and, under certain circumstances, can be more finely distributed and even atomized.

The dampening water supply can be straight or curved and can be arranged parallel or obliquely in the reactant supply. In this way, there are different distances between the first and second openings and, as a result, different amounts of the first openings directly into the assigned reactant distribution rooms humidification water. Basically, the following applies: the smaller the water drops emerging from the first openings, the greater the distance between the first and second openings and the faster the reactant flow rate, the greater the

Proportion of dampening water droplets that are diffusely fed into cells downstream of the respective outlet openings.

The feed for the reactant, with the aid of which the humidification water reaches the individual fuel cells, can be designed in different ways. According to one embodiment, the reactant supply can be constructed from individual sections, each of which opens into the reactant supply space for the reactant in question for each individual fuel cell, and can be passed through the remaining area of each individual fuel cell, against the

Transition of reaction gas must be sealed in a conventional manner. Alternatively, the reactant supply, into which the dampening water is introduced, can be designed as a line which runs through the entire fuel cell stack and which has second openings in the region of the reactant distribution spaces of the individual fuel cells, ie openings for the outlet of reactant and dampening water. These openings are preferably as large as possible in order to ensure an adequate dosage of reactant and dampening water. Particularly if only openings of a defined size are available for the transfer of reactant and dampening water into a reaction medium distribution space, it is preferred that the first openings in the dampening water supply are essentially in the region of the second openings of the reactant supply. Otherwise there is one certain displacement of the openings in the dampening water supply relative to the openings in the reactant supply is harmless, especially when the openings in the dampening water supply are displaced upstream of the openings in the reactant supply. The reason for this is that a reagent flowing at high speed can move a water drop emerging from an opening of the dampening water supply in the direction of flow and does not bring it completely into the associated reagent distribution space, but rather entrains part of the water drop and therefore becomes trapped in the course of the passage through the

Fuel cell stack enriched with the finest droplets of dampening water.

When the dampening water is introduced according to the invention, part of a drop of water emerging from the dampening water supply is thus precisely introduced into the reagent distribution space to be humidified, while part of the water drop is transported downstream with the reagent, the reagent is increasingly loaded with water and thus for a stronger moistening due to diffuse in the reagent distributed water of the individual fuel cells further downstream. This greater humidification of individual fuel cells located further downstream is an additional advantage of the present invention, which is particularly useful for stacks with a larger number of individual fuel cells, but can also be useful for stacks with only a few individual fuel cells. The

Individual fuel cells in a stack are not operated under completely identical conditions, but differ in particular with regard to their operating temperature. Cells inside a stack are usually at a higher temperature than the more am Cells arranged at the edge of the stack. The difference between the hottest and coldest cell in a stack can easily be 5 to 15 Kelvin. Accordingly, the polymer electrolyte membranes of the cells in the interior of a stack have a greater tendency to dry out and therefore have a higher need for dampening water than that of the outer cells of the

Case is. By introducing dampening water according to the invention, these cells are automatically moistened more in the central region of a stack. In order to avoid an oversupply of humidification water in the case of the individual fuel cells located even further downstream, that is to say the cells arranged at the opposite end of the stack, fewer water outlet openings per individual fuel cell can simply be provided. If, for example, the dampening water supply has two water outlet openings per individual fuel cell from the beginning of the stack to the middle region of the stack, it is often sufficient at the end region of the stack, only one

Provide water outlet opening for each fuel cell. The dampening water supply can also be arranged further away from the inlet openings into the reactant distribution spaces in the end region, so that less water is fed directly into them, but more water is diffusely distributed in the reactant and also leaves the stack with the reactant flow emerging from the stack.

In general, by choosing the right arrangement, size and number of water outlet openings in the dampening water supply, the dampening water requirement in each area of the fuel cell stack can be optimally adapted to the requirements. For example, in certain areas of the stack, additional openings between the individual fuel cells can be provided in the dampening water supply. can be seen, or the dampening water supply can already contain openings before entering the stack, or water outlet openings can be completely absent in the downstream end region of the stack.

Another, particularly preferred option, according to your

Arrangement in the fuel cell stack to optimally satisfy the different humidification water requirements of the individual fuel cells consists in supplying the reactant transporting the humidification water to the fuel cell stack from both sides. The water droplets emerging from the humidification water supply are then increasingly fed by the flowing reactant from both ends of the stack to the middle, hotter region of the stack, while only a little less humidification water is available at both end regions of the stack.

In this way it is ensured that each individual cell in the fuel cell stack is precisely metered in the required amount of dampening water and the reaction gas stream ensures the uniform water distribution in the individual cells. There are no areas with undersupply, as is the case, for example, with an external metering of dampening water into the reactant gas stream, or areas with oversupply, as is the case with vaporous humidification water supply, if an undesired partial condensation occurs in colder end areas of the stack of the dampening water vapor.

The humidification water supply can be operated with continuous flow or in "dead-end operation". With continuous Flow it makes sense to return the unused dampening water.

The lines for the reactants and humidification water are preferably brought together in the end plates of the stack, but can also be carried out beforehand without further ado. The combined reactant / dampening water supply line is then preferably guided through the stack in such a way that gravity can be used to distribute the dampening water in addition to the kinetics of the volume of reactant. It is therefore preferred to carry it out in the upper edge area or in an upper corner area of the fuel cell stack, with a diagonal flow of the reactant and dampening water through the individual fuel cells. In the case of fuel cells with a suitable sealing edge, for example with an integrated sealing edge, as described in WO 98/33225, the combined reactant / dampening water supply can also be integrated into the sealing edge, so that no active reaction area is lost.

The humidification water supply according to the invention is fundamentally suitable for every type of fuel cell. A particularly good distribution of the

Humidification water, and thus a particularly homogeneous humidification, is achieved if a flow channel structure is present in the reagent distribution space. This flow channel structure can be provided separately or can be part of the electrode or the bipolar plate delimiting the cell or other delimitation.

The control of the dampening water metering is based on the operating parameters of the fuel cell system. The need for humidification water is determined, for example by measuring the interior Resistance of the polymer electrolyte membranes, but preferably by monitoring the temperature and / or performance of the fuel cell stack. Monitoring of the voltage level is also possible. For the measurement of temperature, power, voltage or even the internal resistance, selected reference single cells or the whole can be used

Stacks can be used. According to the determined need, dampening water is fed from a storage container to the fuel cell stack via a pump, preferably a membrane pump, and a valve, preferably a solenoid valve. A coupled mode of operation of the pump and the solenoid valve is advantageous to the preferred pulse-like

To achieve metering. The excess dampening water emerging from the fuel cell stack via the reactant discharge line can be fed back to the storage container together with the water of reaction formed via a water separator, as a result of which the water consumption can be minimized.

The simple construction of the apparatus makes it possible to react to changes in the stack temperature, the stack output or the stack tension in a matter of seconds and to adapt the dampening water metering exactly to the requirement profile. Alternatively, for one

Characteristic fuel cell stacks are created, which then make it possible to adapt the water metering to the requirement profile with an exact knowledge of the fuel cell behavior. If, for example, a system runs through a known power cycle, the dampening water supply can be regulated in good time in anticipation of each operating state to be expected. In this way, the amount of dampening water is not adapted to every operating state with a slight delay, but when a the right amount of humidifying water is always available.

In operation, only the humidification water reservoir and the feed line are filled with humidification water, so that the humidification system according to the invention with little effort, for. B. for heating and insulation, frost-proof. The humidification water supply within the fuel cell stack is intrinsically safe against freezing, since the water has sufficient expansion options due to the existing water outlet openings.

The dampening water supply preferably consists of electrically non-conductive material, e.g. made of PTFE. Additives that are required, for example sulfonic acid groups dissolved in water, can be added to the dampening water in order to increase the long-term stability of the polymer electrolyte membranes.

The invention is described in more detail below with the aid of preferred embodiments. The humidification water supply is shown in combination with the fuel gas supply. However, the combination with the oxidant supply or the introduction of dampening water into both reactant streams is equally possible.

The drawings show:

Fig. 1 shows an embodiment of a single fuel cell

Stack with dampening water supply according to the invention, 2 shows a partial area of a fuel cell stack with dampening water supply according to the invention,

3 shows a section through the arrangement of FIG. 2 in the plane of a reagent distribution space of a single fuel cell,

4a, 4b each and every one of the various embodiments of arrangements of dampening water supply and reactant supply according to the invention,

5a-5e different embodiments of arrangements according to the invention of the first openings in the dampening water supply,

Fig. 6 is a schematic representation of the basic structure of the dampening water supply system according to the invention.

1 shows a single fuel cell 2 with a dampening water supply according to the invention. The line 12 for the dampening water supply is arranged inside and on the upper edge of the line 10 for the fuel gas supply. As a result, most of the fuel gas flow G is available for the distribution and division of the dampening water. The line 10 for the fuel gas supply (with line 12 in it for supplying dampening water) is in turn arranged at the upper edge of the individual fuel cell 2, so that in addition to the kinetics of the gas flow, gravity can also be used to distribute the dampening water. The single fuel cell shown consists of anode 3 (with catalyst), cathode 5 (with catalyst) and polymer electrolyte membrane 7 arranged between them. On the surfaces of the anode 3 and cathode 5 facing away from the polymer electrolyte membrane there are an anode-side reactant distribution space 4 and a cathode-side reactant distribution space 6

Distribution of fuel gas in the anode area and oxidizing agent in the cathode area. The reagent distribution space 4 has a width 19, and the line 10 for the supply of bromide gas has an opening 17 in this area, so that fuel gas can enter the fuel gas distribution space unhindered. The line 12 for the humidification water supply has an opening 15 in the area of the opening 17 of the bremgas supply line, through which humidification water enters the fuel gas line 10 in droplet form, is captured by the fuel gas, divided and taken along on the way to the fuel gas distribution space 4, where it comes together is evenly distributed with the fuel gas and via the anode

3 reached the polymer electrolyte membrane at 7.

2 shows a detail from a fuel cell stack 1 with a plurality of polymer electrolyte individual fuel cells 2, stack end plate 13 and dampening water supply according to the invention. The structure of the

Individual fuel cells 2 and the dampening water supply are in principle as described in FIG. 1, the individual fuel cells being indicated only schematically in FIG. 2. For each individual fuel cell 2, however, the fuel gas distribution space 4 is shown, and it can be seen that the line 12 for supplying dampening water in the area of the fuel gas distribution space 4 of each individual fuel cell 2 has an opening 15 for the discharge of dampening water. The fuel gas supply 10 is not a continuous line, but consists of sections that pass through the areas of the individual cells. go through, into which no fuel gas may enter, but leave the area of the fuel gas distribution spaces 4 free, ie have interruptions 18 there. If seals are provided between the individual cells, they can be shaped so that they are part of the line 10. The combination of fuel gas line 10 and dampening water line

12 was done before entering the fuel cell stack.

Fig. 3 shows a section through the arrangement of Fig. 2 in the plane A-A ', i. that is, a section through a fuel gas distribution space 4. The embodiment shown here contains a flow channel structure 8 for better distribution of humidification water and fuel gas in the fuel gas distribution space 4. The line 10 for the fuel gas supply has an oval shape, and a round line 12 running inside it arranged for humidification water supply. The line 12 has openings 15 in the lower region through which dampening water enters the flow channel structure 8.

4a shows an embodiment according to the invention of a combined dampening water / reactant supply. The round line 12 for supplying dampening water is arranged inside and in the upper region of the oval line 10 for supplying the reactant. The lines 10 and 12 each have the same spacing on their undersides, and are arranged substantially congruently, first openings 15 and second openings 17 for the escape of water or water / - reactant. The distances between the openings 15 and the

Distances between the openings 17 correspond to the distances between the reactant distribution spaces 4. 4b shows another embodiment of a dampening water / reactant supply according to the invention. In this embodiment, the line 12 for the supply of dampening water is not arranged inside but directly above the line 10 for supplying the reactant. In this "piggyback" version, the two are

Lines 10 and 12 are connected via the openings 15, which are passages here.

In Figures 4a and 4b, the lines 10 and 12 are each shown round or oval, but they can basically be any

To have shape.

5a shows a downstream end region of a combined dampening water / reaction mixture feed according to the invention of a fuel cell stack. The openings 17 in the reactant supply are shown relatively small here and in the other embodiments shown. Wider openings 17 allow the humidification water to be introduced more reliably into the reaction medium distribution spaces, since the system becomes less sensitive to drifting of the water drops emerging from the openings 15 due to the gas flow G as the width of the openings 17 increases. Inaccurate matching of openings 15 and openings 17 is then less important. In general, the openings 17 can extend in the flow direction at most over the width 19 of the reaction medium distribution spaces 4.

The openings 17 can extend perpendicular to the direction of flow at most over the entire circumference of the reactant supply 10. In this limit case, the openings 17 go into the interruptions 18 over, ie the reactant supply consists of individual sections.

In the embodiment shown in FIG. 5 a, the stack end plate 14 located downstream is located immediately adjacent

Area of the dampening water supply 12 no more openings 15. In the end region of the stack, the reactant has taken up sufficient dampening water on its way through the stack to supply the last two cells of the stack with dampening water. Alternatively, the distance between openings 15 and associated openings 17 can also be increased.

5b shows an upstream end region of a combined dampening water / reactant supply line according to the invention of a fuel cell stack. Reagent supply 10 and

The dampening water supply duct 12 was brought together on the upstream stack end plate 13 before it entered the fuel cell stack. The dampening water duct 12 already has water outlet openings 15 shortly before it enters the fuel cell stack. As a result, the reactant takes immediately before its

Entry into the dampening water fuel cell stack. This embodiment is particularly useful in the case of very fast reactant flows G when there is a risk that the cells 2 in the initial region of the stack will not be adequately supplied with dampening water, since the rapid reactant flow will cause a considerable part of each drop of water emerging from an opening 15 before it enters the associated reagent distribution space with it. Alternatively, the dampening water supply can also be attached closer to the openings 17 in the initial area than in further downstream areas of the stack, so that a larger part of the water drops emerging from the openings 15 enters the assigned openings 17 directly.

5c shows a central region of a combined dampening water / reactant supply according to the invention. As shown here by way of example for the middle single fuel cell, the dampening water supply duct 12 in the area of the single fuel cells 2 with increased moisture requirement can have several openings 15 per opening

17 of the reactant supply 10 have. The more humidification water outlet openings 15 are in the area of an opening 17 or interruption 18 leading into the reagent distribution space 4 of an individual fuel cell 2, the more humidification water is supplied to the corresponding individual fuel cell 2. Alternatively, the dampening water supply can be attached closer to the openings 17 than in other areas of the stack.

5d also shows a region of a combined dampening water / reactant agent according to the invention which is located in the center of the stacker.

Zuführang. Here, too, additional water outlet openings are provided in the dampening water supply duct 12 in the area of the fuel cells with increased dampening water requirements. In contrast to FIG. 5c, however, the additional water outlet openings here are not exactly assigned to a specific individual fuel cell. Rather, additional water outlet openings 16 distributed between the water outlet openings 15 are provided in the central region of the dampening water supply duct 12. The water emerging from the openings 16 becomes taken up by the reactant flow G and diffusely distributed to the subsequent individual fuel cells.

FIG. 5e shows a combined dampening water / reactant supply line according to the invention, as shown in principle in FIG. 4a. In

5e shows the effects of a two-sided supply of reactant. The water drops emerging from the openings 15 of the humidification water line 12 are broken up by the flowing gas G and partly fed into the fuel cell assigned to the respective outlet opening 15, but partly also from the

Gas flow torn away, so that the gas flow accumulates a little more with water droplets as it passes through each opening 15. This happens from both ends of the stack. In this way, an increased amount of dampening water is automatically available in the middle, hotter area of the stack.

6 shows a fuel cell system according to the invention with preferred peripherals. A combined moistening water 12 / reactant 10 supply leads into the fuel cell stack 1. The humidification water is fed into the fuel cell stack 1 from a reservoir 25 via a membrane pump 26 and a solenoid valve 27. Pump 26 and solenoid valve 27 operate coupled to achieve the preferred pulsed metering range. The excess dampening water emerging from the stack 1 via the reaction gas discharge line is returned to the reservoir 25 together with the water of reaction formed via a return line 28 with a water separator 29. Here too, of course, it applies that the dampening water supply line can not only take place on the fuel gas side, as shown, but also on the oxidant side or on both sides. The type of fuel cell humidification according to the invention has a number of advantages over conventional systems:

The construction is very straightforward and requires little equipment. In the fuel cell stack itself, only simple lines with openings are required, and, in addition, all that is required is a reservoir for dampening water, a metering device in the form of a pump and metering valve and, if appropriate, a device for measuring the cell temperature, voltage or power. Such a compact system can also be easily insulated and designed to be frost-proof.

The system has a low consumption of dampening water and the dampening water does not require any preconditioning. On the one hand, this simplifies the structure of the system, and on the other hand it keeps it

Low energy consumption. The system can basically be operated at any temperature at which the dampening water is in the liquid state. As a rule, the dampening water can therefore simply be fed in at the respective ambient temperature. If temperatures are unsuitable, the system is easy to isolate, heat or cool due to its compactness.

In the case of the fuel cell humidification according to the invention, the individual amount of humidification water required is metered into each individual cell only in a stack. Even with large temperature differences in the stack, there are no areas with undersupply or oversupply of dampening water. The regulation of the dampening water metering according to the operating parameters of the fuel cell stack is simple, precise and extremely dynamic. It can be adapted to changing operating conditions in a matter of seconds. Forward-looking operation is also possible.

The humidification water supply can also be used to supply any auxiliary materials required.

Claims

PATENT CLAIMS

Fuel cell stack (1) with a plurality of polymer electrolyte membrane individual fuel cells (2) and with feeds for reactants (10, 11) and dampening water (12), each individual fuel cell (2) having an anode (3), a cathode (5), one in between has arranged polymer electrolyte membrane (7) and an anode-side (4) and / or cathode-side (6) reactant distribution space, characterized in that at least one humidification water inlet (12) is arranged through the fuel cell stack and has a plurality of first openings (15), at least one supply of reactant (10, 11) through the

The fuel cell stack (1) is arranged to lead through and has a plurality of second openings (17) or interruptions (18), the at least one dampening water supply (12) being connected to the at least one reactant supply (10, 11) via the plurality of first openings (15) and the at least one reactant supply (10, 11) is connected via the plurality of second openings (17) or interruptions (18) to the anode-side (4) or cathode-side (6) reaction medium distribution spaces of the individual fuel cells (2).

2. Fuel cell stack (1) according spoke 1, characterized in that the dampening water supply (12) is arranged in the interior of the reactant supply (10, 11).

3. Fuel cell stack (1) according spoke 1, characterized in that the dampening water supply (12) and the reactant supply (10, 11) are arranged immediately adjacent to each other.

4. The fuel cell stack (1) according to one of claims 1 to 3, characterized in that the reaction gas supply line (10, 11) connected to the dampening water supply line (12) is the fuel gas supply line (10).

5. Fuel cell stack (1) according to one of claims 1 to 3, characterized in that the with the dampening water supply (12) in connection Reaction Nύttekuführang (10, 11) is the oxidant supply (11).

6. Fuel cell stack (1) according to one of claims 1 to 3, characterized in that it has at least two humidification water supplies (12), each with a reactant supply (10, 11) in connection, wherein a reactant supply the fuel gas supply (10) and a reactant feed is the oxidant feed port (11).

7. Fuel cell stack (1) according to one of claims 1 to 6, characterized in that the first openings (15) in the dampening water supply (12) and the second openings (17) or interruptions (18) in the reactant supply are arranged essentially overlapping.

8. Fuel cell stack (1) according to one of claims 1 to 7, characterized in that the first openings (15) in the

The dampening water supply (12) has a round shape with a diameter of 0.1 to 1.0 mm.

9. Fuel cell stack (1) according to one of claims 1 to 8, characterized in that the moistening water supply duct (12) has additional water outlet openings (16) in the part (23) located in the central region of the stack.

10. Fuel cell stack (1) according to one of claims 1 to 9, characterized in that flow channel structures (8, 9) are provided in at least one of the reagent distribution spaces (4, 6) for better distribution of the reagent and dampening water.

11. Fuel cell stack (1) according to one of claims 1 to 10, characterized in that the dampening water supply (12) consists of electrically non-conductive material.

12. Fuel cell humidification system, comprising a fuel cell stack (1) according to one of claims 1 to 11, a dampening water reservoir (25), a dampening water pump (26), and if desired, a device (27) for the pulsed supply of dampening water and one Device for returning dampening water (28).

3. Method for moistening at least one reactant in a fuel cell stack (1) with a plurality of polymer electrolyte membrane individual fuel cells (2) and with feeds for reactants (10, 11) and dampening water (12), each individual fuel cell (2) having an anode (3 ), a cathode (5), a polymer electrolyte membrane (7) arranged therebetween and an anode-side (4) and / or cathode-side (6) reaction medium distribution space, characterized in that at least one dampening water inlet (12) is provided with a plurality of first openings (15) over which the

Humidification water supply (12) is connected to a reactant supply (10, 11) in which a plurality of second openings (17) or interruptions (18) is provided via the reaction water supply connection (10, 11) connected to the dampening water supply (12) the Reactionsrmttelzufuhrang communicates with the anode-side (4) or cathode-side (6) reactant distribution spaces of the individual fuel cells (2), and dampening water in liquid form - is fed into the dampening water supply (12) via the first openings (15) into the reactant supply (10, 11) occurs, from which the reactant flowing in the reactant feed (10, 11) is taken up, and - together with the reactant into the anode side

(4) or cathode-side (6) reactant distribution spaces of the individual fuel cells (2) is fed.

14. The method according to claim 13, characterized in that the dampening water is fed in pulse.

15. The method according to claim 14, characterized in that the dampening water is fed with a pulse rate of 1 pulse per 1 to 120 s and a pulse duration of 0.5 to 10 s.

16. The method according spoke 15, characterized in that the dampening water is fed with a pulse rate of 1 pulse per 10 to 40 s and a pulse duration of 0.8 to 2.0 s.

17. The method according to any one of claims 13 to 16, characterized in that the dampening water is fed into the fuel gas.

18. The method according to any one of claims 13 to 16, characterized in that the dampening water is fed into the oxidizing agent.

19. The method according to any one of claims 13 to 16, characterized in that dampening water is fed into both the fuel gas and the oxidizing agent.

20. The method according to any one of claims 13 to 19, characterized in that the reactant absorbing the dampening water is fed from both ends of the stack (1) into the reactant supply (10, 11).

21. The method according to any one of claims 13 to 20, characterized in that the dampening water is introduced into the reactant distribution spaces (4, 6) and distributed in them using the reactant volume flow and gravity.

22. The method according to any one of claims 13 to 21, characterized in that the Humidification Wasser∑aiführang (12) takes place in dead-end operation.

23. The method according to any one of claims 13 to 21, characterized in that the dampening water supply is operated with a continuous flow, preferably with dampening water recirculation.

24. The method according to any one of claims 13 to 23, characterized in that the fuel cell stack (1) is operated at a pressure from atmospheric pressure to 400 kPa gauge pressure.

25. The method according to any one of claims 13 to 24, characterized in that the pressure in the humidification water supply (12) is 10 to 50 kPa above the pressure in the reactant supply (10, 11), in the case of pressure peaks with pulsed feeding also above.

26. The method according to any one of claims 13 to 25, characterized in that the dampening water supply is anticipated regulated operating conditions.

7. The method according to any one of claims 13 to 26, characterized in that the dampening water emerging from a first opening (15) of the dampening water supply duct (12) through an opening (17) associated with the first opening (15) or interruption (18) of the reactant supply Guide (10, 11) in the anode-side (4) or cathode-side (6) reagent distribution space, with which it is connected, is fed and / or diffusely distributed in the reagent feed (10, 11) and one or more downstream reagent distribution spaces (4, 6) is supplied.