DE102013004799A1 - Humidifying device for humidifying process gases and fuel cell assembly comprising such - Google Patents

Abstract

The invention relates to a humidification device (50) for humidifying process gases, in particular for fuel cells (12), comprising a stack (52) of repeating components, comprising a) a water vapor permeable membrane (60), b) one, on a first side of the membrane (60) arranged first layer arrangement (70), comprising a first flow layer (72) for conducting a process gas to be humidified, which comprises a plurality of flow webs (74) running parallel to the membrane (60), which delimit flow channels (76), and c) a second layer arrangement (80) arranged on a second side of the membrane (60), comprising a second flow layer (82) for conducting a damp gas, which comprises a plurality of flow webs (84) running parallel to the membrane (60), which flow channels (86 ) limit. According to the invention, at least some of the flow webs (84) of the second flow layer (80) are designed with a plurality of stabilization points (88) in the form of local enlargements of the web widths (B) with respect to a plane running parallel to the membrane (60).

Description

The invention relates to a humidifying device for humidifying process gases, in particular for fuel cells, and to a fuel cell arrangement comprising such a humidifying device.

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 two sandwiching the membrane enclosing electrodes (anode and cathode). As a rule, the fuel cell is formed by a multiplicity of stacked MEAs whose electrical powers add up. During operation of the fuel cell, the fuel, in particular hydrogen H ₂ or a hydrogen-containing gas mixture, is supplied to the anode, where an electrochemical oxidation takes place with emission of electrons (eg H ₂ → 2H ⁺ + 2e ^- ). Via 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 in the cathode compartment. The electrons provided at the anode are fed to the cathode via an electrical circuit. The cathode is also supplied with oxygen or an oxygen-containing gas mixture, so that a reduction of oxygen taking up the electrons takes place (1/2 ₂ + 2e ^- → O ^2- ). At the same time, the oxygen anions formed in the cathode compartment react with the protons transported via the membrane to form water (O ^2- + 2H ⁺ → H ₂ O). The direct conversion of chemical to electrical energy fuel cells achieve over other electricity generators due to the circumvention of the Carnot factor improved efficiency.

The focus of current fuel cell development is particularly directed to traction applications for propulsion of motor vehicles. The most advanced fuel cell technology currently available is based on polymer electrolyte membranes (PEMs), in which the membrane is formed from a moistened polyelectrolyte (eg ^Nafion® ) and the water-bonded electrolytic conduction takes place via hydrated protons. Such polymer electrolyte membranes are dependent on the presence of water for proton conduction. Below a certain temperature, the cathodically formed product water as a source of moisture for moistening the membrane can still be sufficient for this purpose. At higher temperatures, however, moisture is increasingly being discharged from the fuel cell stack with the cathode exhaust gas. To counteract dehydration of the fuel cell membrane here, the moisture must be compensated by active supply of water.

WO 98/45889 A1 describes a fuel cell with internal water supply, in which both the fuel gas in the anode region and the air in the cathode region water is added in the form of an aerosol. The introduction takes place via the channels of the respective bipolar plate.

Also DE 10 2005 025 914 A relates to the internal humidification of a working medium of a fuel cell. For this purpose, the bipolar plate of the fuel cell is equipped with webs which separate the inflowing medium flow and the outflowing medium flow from each other. The webs are interrupted by sections formed by a water vapor permeable membrane.

Furthermore, it is known to use external humidifying devices in order to moisten the process gas to be supplied to the fuel cell, in most cases the air to be supplied to the cathode compartments. In particular, part of the moisture discharged from the stack with the exhaust air of the cathode compartments is recycled. The moisture recirculation strategy is realized for PEM fuel cells either by way of water diffusion over water vapor permeable membranes and / or by the capillary principle through the finest channels of a porous layer. So-called hollow fiber modules are suitable for the diffusion principle and also for the capillary principle. Membrane humidifiers utilize the product water formed by the fuel cell reaction at the cathode using a water vapor permeable membrane to humidify the process gas to be supplied to the fuel cell. In this way, not only the drying of the membrane is prevented, but also an excessive accumulation of water in the fuel cell.

US 2008/0241636 A1 ( DE 10 2008 016 087 A1 ) describes such a membrane humidifier, which is designed according to the principle of a countercurrent heat exchanger, wherein a steam-rich gas is passed through lines which are enclosed by a housing through which a gas mixture to be humidified flows in countercurrent. The lines consist of a water vapor permeable membrane material.

Out DE 10 2009 005 685 A1 For example, an external membrane humidifier is known which comprises a stack of corrugated sheets each having a membrane disposed therebetween. Through the corrugated plates flow channels formed, which are partially flowed through by the wet cathode exhaust gas and partly by the cathode air to be humidified. The membrane is contacted on both sides by a respective layer of a hydrophilic diffusion medium which, on the one hand, absorbs the water and is to transport it to and from the membrane and, on the other hand, structurally supports the membrane.

US 2009/0092863 A ( DE 102008 050 507 A1 ) describes a membrane humidifier having a stack of alternating wet plates and dry plates, between each of which a water vapor permeable membrane is arranged. Each wet and dry plate consists of two gas diffusion layers, between which webs are arranged, which delimit flow channels. The flow channels of the wet plate carry moist exhaust air from the cathode side of the fuel cell and the flow channels of the dry plate lead relatively dry process gas, which is supplied to the fuel cell. The plates are laterally sealed by solid plastic strips.

In WO 2009/101036 A1 Instead of such gas diffusion layers supporting elements are used from a mesh fabric, so that the membrane is supported at least on the dry side or on both sides of a mesh fabric. As a result, the freely accessible contact surface of the membrane is to be increased.

In the US 2008/0001313 A1 disclosed membrane humidifier correspond to those described above, but have other channel structures. Instead of webs, here the channels of the wet and dry plates are produced by plates with corrugated metal structure or by plates with double-sided grooves. A similar structure is out DE 10 2010 035 359 A1 known.

In the external humidifiers with plate-like structure, the support of the membrane on its low pressure side, so the humid exhaust air side is required in order not to deform or even damage the membrane due to the pressure acting from the high pressure side. For this purpose, a gas-permeable supporting layer (diffusion layer) is usually arranged between the low-pressure flow layer and the membrane. This is usually a fleece made of plastic, carbon or glass fibers or the like and is intended to ensure the highest possible gas transport rate.

In order to further allow the largest possible contact surface of the gas with the water vapor permeable membrane and thus a high Befeuchtungsrate, it is generally desirable to dimension the web widths of the flow webs which limit the flow channels as small as possible, and thus to increase the flow cross section of the channels and to reduce pressure losses. The reduction of the web widths, however, are limited by the fact that a sufficient and uniform contact pressure of the webs on the Stützschich / diffusion layer must be ensured. In addition, very narrow webs tend to dodge and twist with not exactly vertical force and can thus cause a deformation of the low-pressure layer arrangement.

The invention is based on the object of proposing an external humidifying device for humidifying process gases, in particular fuel cells, which ensures a larger free contact area of the water vapor permeable membrane and thus a higher moisture transfer rate to the process gas to be humidified.

This object is achieved by a humidifying device for humidifying process gases and a fuel cell assembly comprising the same having the features of the independent claims.

• a) eine wasserdampfpermeable Membran,
• b) eine, auf einer ersten Seite der Membran angeordnete erste Schichtanordnung, umfassend eine erste Strömungsschicht zur Leitung eines zu befeuchtenden Prozessgases, die eine Vielzahl parallel zur Membran verlaufender Strömungsstege umfasst, welche Strömungskanäle begrenzen, und
• c) eine, auf einer zweiten Seite der Membran angeordnete zweite Schichtanordnung, umfassend eine zweite Strömungsschicht zur Leitung eines Feuchtgases, die eine Vielzahl parallel zur Membran verlaufender Strömungsstege umfasst, welche Strömungskanäle begrenzen.

The moistening device according to the invention comprises a stack of repeating components, comprising:

• a) a water vapor permeable membrane,
• b) a, disposed on a first side of the membrane first layer assembly comprising a first flow layer for guiding a process gas to be humidified, which comprises a plurality of parallel to the membrane extending flow webs which define flow channels, and
• c) a, disposed on a second side of the membrane second layer assembly comprising a second flow layer for conducting a moist gas, which comprises a plurality of parallel to the membrane extending flow webs, which define flow channels.

The moistening device according to the invention is characterized in that at least part of the flow webs of at least the second flow layer is formed with a plurality of stabilization points in the form of local enlargements of the web widths with respect to a plane extending parallel to the membrane.

Due to the local stabilization points of the webs twisting of the flow webs is made difficult or even prevented with not exactly vertical force. At the same time, the stabilization points increase the support surface of the webs and thus ensure a better distribution of force. The stabilizing sites of the invention thus allow a reduction of the web widths and thereby an increase in the operating gas freely accessible membrane surface, without causing insufficient support of the membrane.

In a preferred embodiment, the flow webs of at least the second flow layer web widths of at most 1.0 mm, in particular of at most 0.6 mm, and preferably of at most 0.4 mm. Here, web width is understood to be the width of a web outside the local stabilization points. Despite these small web widths, a sufficiently large contact surface (support surface) for the membrane (or a support layer arranged between membrane and webs) and a high stabilization of the webs are achieved due to the stabilization points of the webs according to the invention. At the stabilization points itself, the web has, for example, a 1.5 to 3 times its other web width, in particular a 2 to 2.5 times.

Preferably, the stabilization points are distributed at equal intervals over the entire length of a flow web. Suitable distances between two stabilization sites are for example 2 to 20 mm, in particular 4 to 10 mm.

According to a further preferred embodiment of the invention, at least the flow webs of the second flow layer at their end portions, that is, at a transition of an active with respect to the wetting effect area of the layer assembly to a peripheral edge region, larger web widths, as at their central portions between the stabilization points , As a result, a further stabilization of the webs with respect to the turning away and a further enlargement of the support surface (support surface) is achieved.

According to a further preferred embodiment of the invention, at least a part of the flow webs of the second flow layer each have at least one local reduction of the web height with respect to a plane extending orthogonal to the membrane. The local reduction of the web height thus corresponds to a partial lowering of the membrane facing web surface. Preferably, each flow land has a plurality of such local reductions in land height. These can also be formed on both sides of the web. Between the local reductions in the web height, ie where the web has its full height, local support points are thus formed for the membrane (or for a support layer running between the membrane and the web). On the other hand, at the points of local reductions of the web height, no contact force is exerted. Rather, this area is available as a free gas exchange surface over the membrane. In this way, the freely accessible membrane surface and thus the moisture transfer rate is further increased. At the same time, the free flow cross section of the flow channels increases due to the partial web height reductions, so that pressure losses are also reduced.

Preferably, no reduction in web height is provided at the stabilization sites, i. H. At the stabilization points, the full web height is available.

The second moist gas-carrying layer arrangement preferably also has two gas-permeable support layers adjoining the flow layer or the flow webs on both sides thereof. The second flow layer is thus sandwiched by two support layers. The support layer has the task of mechanically supporting the membrane on its moist gas-carrying low-pressure side in order to prevent its bulging in the direction of the low-pressure side. On the other hand, the support layer must allow sufficient gas flow of the moist gas to the membrane.

In principle, the gas permeable backing layers may comprise nonwoven materials of suitable fibers, such as plastic fibers, glass fibers or carbon fibers. With particular advantage, however, it is provided in the context of the present invention that the gas-permeable supporting layers are formed as supporting films which have a plurality of passage openings for the passage of gases. The replacement of the nonwoven by the backing film significantly shortens the path of the moist gas to the membrane and also bypasses the flow-braking effect of the nonwoven. Furthermore, by an increased movement of the moist gas in the vicinity of the membrane, the moisture transport can be selectively influenced by the moist gas to the membrane surface. The flow rates can be adjusted to cause turbulence in the flow channels and improve moisture wicking. Another advantage of using the backing film is the incompressibility and stability of a film. Thus, a concavity of the support film in the direction of the low pressure side can be largely avoided. Due to the stable channel geometry thus achieved, pressure losses can also be kept small and predicted more accurately. The prediction of the pressure losses also allows defined turbulent flows within a window of maximum allowable pressure losses, which in turn allow increased moisture transport. In contrast to nonwovens, which can be deformed, yields When using support films also a higher stability in the pressing direction of the stack. This stability can be maintained even after the stack was pressed once during its construction and not constantly a pressing force is exerted on the stack.

According to a preferred embodiment of the invention, the support film in the, the through-openings having active area a free area in the range of 20 to 80%, in particular in the range of 40 to 70%, preferably in the range of 55 to 65%. If the free area lies below the stated lower limits, too little moisture exchange takes place between the moist gas and the membrane. On the other hand, if the free area is above the stated upper limits, the support function of the support film for the membrane is reduced too much. In particular, the preferred range of 55 to 65% free area results in increased water transport rate over conventional nonwovens, which typically have a free area of less than 50%. Due to the higher water transport rate, the required membrane area is reduced, so that with the same water transport capacity a smaller component volume is required.

The passage openings of the support foil can have any desired configurations. Preferably, they have a circular shape, wherein diameters of at most 1 mm, in particular at most 700 microns, preferably at most 400 microns, are preferred. In other words, the free area is preferably distributed to the highest possible number of through openings as small as possible in order to achieve a homogeneous support effect over the entire active area.

It is further preferably provided that the first, the process gas to be moistened layer assembly further comprises two adjoining the first flow layer spacer films, which has a peripheral frame portion and at least one, bounded by the peripheral frame area central recess in the humidification active region of the membrane exhibit. The spacer film thus has the shape of a frame, wherein preferably the entire central, with respect to the wetting effect active area is recessed. According to this embodiment, therefore, the usual in the prior art layer of a diffusion medium on the high pressure side of the membrane is replaced by a film structure. In this way, the previously described advantages of the moistening device according to the invention can be further enhanced.

The backing sheets and / or the spacer sheets preferably comprise, independently of each other, or consist of a metal, a plastic or a composite material. Preferably, a metal is used, in particular a stainless steel.

Independently of one another, the support and / or spacer films used according to the invention have a preferred layer thickness in the range from 20 to 120 μm, in particular in the range from 30 to 100 μm, preferably in the range from 40 to 60 μm. Compared with the usual in the prior art diffusion media, which typically have a layer thickness of about 200 microns, thus a significant reduction of the total layer thickness and thus the component volume can be achieved. The volume of the moistening device is thus reduced not only by the reduced membrane area (see above), but also due to the reduced layer height of the stack.

Thus, preferably, the repeating components of the stack do not comprise a porous layer of a diffusion medium in the form of nonwovens or the like.

According to a preferred embodiment of the invention, the (process gas-carrying) flow channels of a first flow layer and the (moist gas-carrying) flow channels of a second flow layer are aligned in different directions, especially in intersecting directions (cross flow). In this way, a particularly high moisture transmission rate is achieved. In a particularly preferred embodiment, the flow webs and thus the flow channels extend in parallel planes, but offset by 90 ° to each other.

Advantageously, the flow channels of the first and / or the second flow layer are open on both sides. The webs, which limit flow channels, are thereby merely fixed by an edge area surrounding the active area. For example, the first and / or second flow layer can each be formed as a film, in whose center region, which is active with respect to the wetting effect, a multiplicity of longitudinal openings is formed, which are delimited by the flow webs extending therebetween.

In a further preferred embodiment of the invention, at least the components of a first (process gas-carrying) layer arrangement and / or the components of a second (moist gas-carrying) layer arrangement are joined together. This is done in particular by one, on both sides of the flow layer subsequent adhesive layer, in particular adhesives are used on acrylic or silicone-based, preferably acrylic adhesive. Preferably, further are Adhesive layers between the water vapor permeable membrane and the respective subsequent first and second layer arrangement present, in particular adhesives are used on acrylic or silicone-based, here preferably silicone adhesive. In this case, all the adhesive layers are preferably present at least in the peripheral peripheral region which encloses the central area which is active with respect to the wetting effect, so that a seal is achieved here. Compared to sealing strips, as described in the prior art, the formation of adhesive seals has the advantage of producing in the same step as the joining of the various components of the stack together and the sealing of the stack to the outside.

The joining of individual components to one another by applying adhesive layers can take place, for example, in a continuous roll process.

The components comprising water vapor permeable membrane, first layer arrangement (dry layer arrangement) and second layer arrangement (wet layer arrangement) form structural units. A plurality of these structural units are repeated in the stack according to the invention, which - arranged in a suitable housing - represents the core component of the external fuel gas process gas humidifier. The stacking of the components is preferably carried out such that in each case a membrane layer is arranged between each pair of dry and wet layer arrangement. By way of example, the stack comprises the following sequence of components: first layer arrangement / membrane / second layer arrangement / membrane, etc.

The stack according to the invention of the repeating component membrane as well as the first and second layer arrangement is preferably arranged in a holder cassette which effects a fixation and a pressing of the components together. In this case, the stack located in the mounting cassette is preferably arranged in a housing which is designed to connect the plurality of flow channels of the first layer arrangements with a process gas supply, in particular a fuel cell, and the plurality of flow channels of the second layer arrangements with a wet gas line, in particular one Exhaust gas discharge of a fuel cell to connect.

Another aspect of the invention relates to a fuel cell assembly comprising a fuel cell stack having a plurality of cathode and anode sections, an anode process gas supply for supplying the anode sections with fuel, for example hydrogen, and a cathode process gas supply for supplying the cathode sections with a cathode process gas, in particular oxygen or an oxygen-containing one Gas mixture such as air. In this case, the cathode process gas supply and / or the anode process gas supply comprise a humidification device according to the present invention for humidifying the cathode process gas or the anode process gas.

For this purpose, the cathode or anode process gas is in flow communication preferably with the first flow layer of the humidifier and the cathode or anode exhaust gas in flow communication with the second flow layer.

The fuel cell assembly is used in particular for driving a motor vehicle.

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

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

1 a fuel cell assembly with a moistening device according to the invention;

2 a single cell of the fuel cell 1 in a sectional view;

3 a section of a moistening device according to an embodiment of the invention in a sectional view;

4 an exploded view of a damp layer arrangement of a humidifying device according to the invention;

5 Single view of a flow layer of the wet layer arrangement 4 according to a first embodiment of the invention (A: plan view, B: detail view);

6 Single view of a flow layer for a wet layer arrangement according to a second embodiment of the invention (A: plan view, B: detailed view);

7 Single view of a flow layer for a wet film arrangement according to a third embodiment of the invention (A: plan view, B: detailed view, C and D: sectional views);

8th Single view of a flow layer of the support film 4 (A: top view, B: detail view) and

9 a mounting cassette of a moistening device.

In the context of the present application, the term "water vapor-permeable membrane" is understood to mean a membrane which is permeable to gaseous water (superheated steam) and / or partially condensed water (wet steam). At the same time, the membrane should be as impermeable as possible to other gas components, that is to say that they should be as selectively permeable to water vapor as possible. Suitable materials include hydrophilic polymers and polymer composites, such as polyperfluorosulfonic acid, which is available as under the trade name Nafion ^®.

The term "process gas" denotes a relatively low-water vapor (dry) gas or gas mixture, for example a gas or gas mixture to be supplied to the cathode of a fuel cell, in particular oxygen or an oxygen-containing gas mixture such as air, and / or a gas or gas mixture to be supplied to the anode, in particular hydrogen or a hydrogen-containing gas mixture.

Furthermore, the term "moist gas" refers to a relatively water vapor-rich gas or gas mixture whose moisture content is greater than that of the process gas. In particular, the moist gas is a relatively water-vapor-rich (moist) gas or gas mixture removed from the cathode and / or anode space of a fuel cell.

The constituent components of the stack, membrane, flow layer, supporting layer and spacer foil are flat components, in particular foils or plates, in which the dimensions of their two main surfaces are larger by at least one order of magnitude, in particular at least two orders of magnitude narrow edge surfaces. Thus, by adjoining layers is meant that these respective layers connect with each other with their main surfaces. In this case, the components can adjoin one another directly or without another intermediate layer or indirectly, separated from one another by one or more intermediate layers, for example by an adhesive layer.

In the present case, the first layer arrangement according to the relatively dry process gas guided therein is also referred to as a dry layer arrangement and the second layer arrangement corresponding to the relatively moist moist gas guided therein also as a wet layer arrangement.

The basic structure and operation of a fuel cell assembly is first based on the 1 and 2 explained.

In 1 is a fuel cell assembly 10 with a fuel cell stack 12 (also simply called fuel cell), which is a plurality of series connected single cells 14 includes. The fuel cell stack 12 is through two end plates 16 held together on both sides.

A single exemplary single cell 14 is in 2 is shown in more detail. Every single cell 14 comprises a membrane-electrode unit (MEA), each having an ion-conducting, in particular proton-conducting polymer electrolyte membrane 16 (For example, a polyperfluorosulfonic acid membrane of the trade name Nafion ^® ) and two sandwiching the two outer membrane surfaces subsequent electrodes, namely an anode 18 and a cathode 20 , Furthermore, the single cells include 14 between each two MEA arranged bipolar plates 22 , which electrically contact both sides of the MEA composite and ensure the supply of the process gases as well as the discharge of the exhaust gases and the product water. In addition, they separate the individual MEA in the fuel cell stack 12 gas-tight from each other. The bipolar plates 22 have a plurality of inner transport channels, which serve to supply the reaction gases (usually in the case of the anode hydrogen and in the case of the cathode oxygen or air) and the cathode side also the removal of the product water. Materials for sealing and stabilizing the MEA are not shown.

The anode 18 and the cathode 20 are configured in the example shown as gas diffusion electrodes and each comprise a microporous catalyst layer 24 deposited on a gas diffusion layer (GDL) 26 is applied. The catalyst layer 24 comprises a carbonaceous or entirely carbonaceous (graphite) support material which, as actually reactive centers, carries a catalytic material, which is usually a noble metal such as platinum, iridium or ruthenium, or a transition metal such as chromium, Cobalt, nickel, iron, vanadium or tin, or mixtures or alloys of these. On the one hand, the carrier material serves for the electrical connection of the catalytic material and on the other hand acts as a fixing and surface enlarging agent. Function of the GDL 26 it is, a uniform flow of the catalyst layers 24 to ensure with the reaction gases oxygen or air on the cathode side and hydrogen on the anode side. Other configurations of the electrodes can also be used in the context of the present invention. For example, the microporous catalyst layers 24 instead of at the GDL 26 also be applied directly on the membrane surface.

The fuel cell 10 also according to 1 an anode process gas supply 28 for supplying the anode sections of the cells 14 with a fuel, especially hydrogen. The anode process gas supply 28 includes an anode process gas line 30 , which on the one hand with a, in particular a hydrogen tank 32 and on the other hand, with the anode portions of the fuel cell 12 communicates. An inner anode-side channel system of the bipolar plates 22 directs the supplied hydrogen H _{2 to} the anodes 18 the single cell 14 to where it is oxidized with the release of electrons to protons H ⁺ . Via an anode exhaust gas line 34 connected to another anode-side internal channel system of the bipolar plates 22 is the unused residual hydrogen (and through the membrane 16 diffused product water) dissipated. A recirculation line 36 connects the anode exhaust gas line 34 with the anode process gas line 30 so that unused hydrogen can be recycled. The anode exhaust gas recirculation is advantageous because the fuel cell 12 is usually operated with an excess of hydrogen (more than stoichiometrically) with respect to the cathode-side oxygen, so that the hydrogen is not completely converted. The operating pressure and the recirculation rate are via corresponding valves 38 . 40 taxable.

Furthermore, the fuel cell has 10 via a cathode process gas supply 42 with a cathode process gas line 44 and a grant 46 , For example, a pump to air and thus oxygen to the bipolar plates 22 and from there via a cathode-side channel system of the same the cathode 20 be forwarded. Via another cathode-side channel system of the bipolar plates 22 and a cathode exhaust line connected thereto 48 the discharge of the remaining air and the product water takes place.

To ensure adequate humidification of the polymer electrolyte membrane 16 of the single cells 14 the fuel cell 12 to achieve, has the cathode process gas supply 42 furthermore via a moistening device according to the invention 50 for moistening the cathode process gas (air) with partial recycling of the cathode side and over the cathode exhaust gas line 48 from the fuel cell 12 discharged product water. For this purpose, the moistening device 50 both with the cathode process gas line 44 as well as with the cathode exhaust gas line 48 connected. Alternatively or additionally, the anode process gas supply can also be used 28 with a corresponding moistening device 50 be equipped, in which case by the polymer electrolyte membrane 16 diffused and discharged with the anode exhaust product water for humidification of the anode process gas (hydrogen) is used.

Not shown in 1 are other components of the fuel cell 12 For example, a cooling system, temperature and pressure sensors and the like, and electronic control means for controlling the fuel cell 12 and their connected components.

The moistening device according to the invention 50 will be in the 3 to 9 shown in more detail.

3 shows in a sectional view of the moistening device according to the invention 50 a section of a pile 52 repetitive components. These include a water vapor permeable membrane 60 (in 3 are two membranes 60 shown), one on a first side of the membrane 60 arranged first layer arrangement 70 (hereinafter also called dry layer arrangement) and one on a second side of the membrane 60 arranged second layer arrangement 80 (hereinafter also wet layer arrangement).

The dry layer arrangement 70 includes a first flow layer 72 , which are a variety, parallel to the membrane 60 running flow webs 74 comprising a plurality also parallel to the membrane 60 running flow channels 76 define. The flow bridges 74 and flow channels 76 the first flow layer 70 run in the selected representation of 3 perpendicular to the paper plane. In the same way also includes the wet layer arrangement 80 a second flow layer 82 with a plurality parallel to the membrane 60 running flow webs 84 , between which flow channels 86 be formed. The flow bridges 74 and flow channels 76 the dry layer arrangement 70 as well as the flow webs 84 and flow channels 86 the damp layer arrangement 80 preferably run according to the cross-flow principle, that is, in directions which are offset by 90 ° to each other. Accordingly, the flow webs run 84 and flow channels 86 the damp layer arrangement 80 parallel to the paper plane according to the illustration of 3 ,

According to the invention, the flow webs 84 the damp layer arrangement 80 each a plurality of local stabilization sites 88 in the form of local enlargements of the ridge widths (bulges) with respect to a parallel to the membrane 60 extending level are formed. Shape and function will be explained in more detail with reference to the following figures.

The dry layer arrangement 70 with their flow channels 76 serves to conduct a process gas to be humidified, in particular for a fuel cell 12 as they are in the 1 and 2 is shown. Preferably, it serves to conduct a process gas, in particular air, to be supplied to the cathodes of a fuel cell. The wet layer arrangement 80 with their flow channels 86 however, the line of a moist gas, which has a higher humidity than the process gas, in particular the cathode exhaust gas of the fuel cell is used 12 ,

The dry layer arrangement 70 also has two, on both sides of the first flow layer 72 subsequent spacer sheets 78 on. The spacer sheets 78 comprise a peripheral edge portion which defines a central recess, that is, they have the shape of a frame. The function of spacer sheets 78 is, the sensitive membrane 60 in front of a direct contact with the flow webs 74 the dry layer arrangement 70 to protect. In addition, by the generated distance between the webs 74 and the membrane 60 maximizes the free membrane area.

The wet layer arrangement 80 however, has two support sheets 90 on which the second flow layer 82 sandwich. The support film 90 characterized by a large number of small through holes 92 from, for example, may have a circular shape. Task of the support film 90 is the water vapor permeable membrane 60 mechanically supported on its low-pressure side. At the same time it should be as free as possible gas exchange between the flow channels 86 and the membrane 60 enable.

It is understood that the stack 52 as the central component of the humidifier 50 a variety of in 3 Having shown structural units. In this case, alternately the dry layer arrangement 70 and the wet layer arrangement 80 stacked on top of each other, each with a layer of a water vapor permeable membrane 60 is interposed.

In 3 It can also be seen that the stack 52 a central, with respect to the wetting effect active area 54 that is from a peripheral area 56 surrounded by a frame. The actual water vapor transport across the membrane 60 only finds in the active area 54 instead of. The border area 56 has predominantly stabilization and sealing function. Not shown in 3 are adhesive layers, preferably between all layers of the stack 52 are present, in each case in the edge region 56 , so that here a connection of the components with each other and a seal outwards through the adhesive layers.

Details of the structure of the second layer arrangement (wet layer arrangement) 80 as well as their individual components are shown in the following figures.

4 shows the structure of the second layer arrangement (wet layer arrangement) 80 in an exploded view. This is the central flow layer 82 with their flow webs and flow channels on both sides of each one adhesive layer 94 sandwiched. To the adhesive layers 94 in turn, each includes a support layer / support film 90 at. The arrangement concludes with a further adhesive layer in each case 96 from.

The to the flow layer 82 subsequent adhesive layers 94 have in the example shown the same blank as flow layer 82 , ie they also replicate the webs. In an alternative embodiment, however, the active area 54 be adhesive-free, while only the edge area 56 has a continuous adhesive layer. At the to the support film 90 each outer adjoining adhesive layers 96 is exclusively in the peripheral area 56 Adhesive provided during the central active area 54 remains adhesive-free. Typical layer thicknesses for the adhesive layers 94 and 96 are in the range of 0.01 to 0.1 mm. Adhesives are in particular adhesives based on acrylic or silicone in question.

The individual in 4 illustrated layers of the wet layer arrangement 80 are arranged with each other. The disposal can take place, for example, by means of continuous roll processes. It is also advantageous, the outer adhesive layers 96 initially to be coated by a carrier film (paper or plastic) to keep, which only before disposing and pressing with the membrane 60 Will get removed. Subsequently, the structure of the in 4 visible cut edges trimmed to the final dimensions.

5A shows an example of the second flow layer 82 the damp layer arrangement 80 according to a first embodiment of the invention in a plan view before cutting to final dimensions. An enlargement of detail B off 5A shows 5B , Recognizable are in the active area 54 a variety of flow webs 84 the film formed, which intervening flow channels 86 limit. As a material for the film formed as a second flow layer 82 In particular, plastics such as polyether ketones (PEEK), polyetherimides (PEI), polysulfones (PSU) and the like, or metals, in particular stainless steels and light metals such as aluminum or magnesium and their Alloys, in question. Suitable layer thicknesses are in the range of 0.1 to 1.0 mm, in particular from 0.3 to 0.8 mm. In the present example, the layer thickness of the second flow layer 82 and thus the web height (H) 0.5 mm. The flow channels 86 can be generated for example by means of laser cutting or punching out of a continuous film. In the present example, the width of the flow channels ( 86 ) 2.0 mm.

The flow bridges 84 have a web width B (s. 5B ) in the range of 0.2 to 1.0 mm, in particular from 0.3 to 0.6 mm, in the present example of 0.4 mm. According to the invention, the webs 84 stabilization points 88 on. These are designed as local enlargements of the web width B. The stabilization sites 88 are preferably distributed at regular intervals over the individual web lengths, here with a distance of, for example, 6 mm. A particularly uniform support effect is achieved when, as shown, the stabilization sites 88 two adjacent bridges 84 offset from one another. The stabilization sites 88 may have any shapes, such as a round shape. The stabilization sites 88 allow a comparison with known designs reduced web width B, since the stabilization points 88 an undesirable twisting of the cross-sectionally rectangular webs 84 prevent, especially if the contact pressure in the stack is not exactly perpendicular to the webs 84 acts. In addition, the stabilizers represent 88 locally enlarged support surfaces for the support layer 90 and thus for the membrane 60 so that the entire support surface is increased.

In the in 5B illustrated embodiment, the flow webs 84 at their end sections 98 Web widths, which are opposite to the general web width B of the middle sections between the stabilization points 88 For example, increased by a factor of 1.5 or more. In the example shown, the width of the webs 84 at the end sections as well as the width of the webs 84 at the stabilization sites ( 88 ) 1.0 mm. Through the widened end sections 98 will further stabilize the bars 84 achieved against twisting and further enlargement of the support surface.

6 shows a further embodiment of a flow layer according to the invention 82 for a wet layer arrangement 80 , Unlike the in 5 Example shown have the flow webs 84 no widened end sections (see detail A in 6B ). In addition, the same characteristics apply with regard to 5 were discussed.

7A shows yet another inventive embodiment of a flow layer 82 for a wet layer arrangement 80 , The training of the webs 84 and the stabilization sites 88 Corresponds essentially to the preceding examples, as in the detail view 7B is recognizable.

A sectional view of a single bridge 84 according to section AA after 7B is in 7C to see. Unlike the ones in the 5 and 6 Examples shown have the flow webs 84 no uniform web height H up. Rather, the webs have 84 local reductions 100 the ridge height H with respect to an orthogonal to the membrane 60 extending level. In this way, between the bridge height reductions 100 So, where, where the webs 84 have their full web height H, supporting surfaces 102 for the membrane 60 or the support film 90 educated. According to 7C are the sections between each two stabilization points 88 with such a ridge height reduction 100 formed so that at the stabilization sites 88 at the same time supporting surfaces 102 for the support film 90 available. At the footbridge height reduction 100 between the support surfaces 102 has the support film 90 no contact with the jetty 84 ,

Basically, the entire support surface of the flow layer 82 to choose so that a sufficient contact surface and thus sufficient support effect for the membrane 60 and the backing sheet 90 is guaranteed. It could be shown that a selective support of the film 90 is sufficient, as long as the forces occurring at these support points by the pressure difference between the dry layer arrangement 70 and the wet layer arrangement 80 can be included.

For example, the ridge height may be at the location of a ridge height reduction 100 be reduced by 0.1 mm from the full web height H. For a film thickness of the flow layer 82 and thus a full web height H of z. B. 0.5 mm is the web height at the location of the ridge height reduction 100 thus 0.4 mm.

An alternative embodiment of a flow web 84 with bar height reductions 100 is in 7D shown on a sectional view. Here the ridge height reductions extend 100 not over the entire sections between two stabilization points 88 , Rather, the ridge height reductions 100 arranged so that even between the two illustrated stabilization sites 88 additional support surfaces 102 be formed.

8A shows an example of a support sheet 90 out 4 in plan view, in their active area 54 a variety of openings 92 having. In the detailed representation in 8B It can be seen that in the present example, the openings 92 have a circular shape. According to the present embodiment, the through holes 92 a diameter of 0.6 mm, with one surface in the active area 78 about 58%. The layer thickness of the support film 90 here is 0.05 mm. For the materials basically come in connection with the flow layer 82 discussed materials, especially stainless steel.

9 shows further details of the structure of the moistening device according to the invention 50 , Accordingly, the pile is 52 , of which only a single dry or wet layer arrangement is shown here by way of example, in a mounting cassette 104 between two end plates 106 arranged. The many dry or damp layer arrangements and the membranes arranged between them in the cassette 90 sealingly pressed together.

The mounting cassette 104 with the humidifier stack inside 52 is then arranged in a housing, not shown, which has connections for the fuel cell to be supplied and to be humidified process gas and for the discharged from the fuel cell moist exhaust gas. For example, the dry process gas by the in 9 overhead open side surface of the cassette 104 in the pile 52 introduced and derived from the bottom side of the cassette. On the other hand, the relatively humid exhaust gas of the fuel cell may leak through the front open side of the cassette 104 in the pile 52 initiated and derived by the rear side open in the diagram. To separate the corresponding spaces, the housing may have appropriate seals.

LIST OF REFERENCE NUMBERS

10

A fuel cell assembly

12

Fuel cell stack (fuel cell)

14

single cell

16

Polymer electrolyte membrane

18

anode

20

cathode

22

bipolar

24

catalyst layer

26

Gas diffusion layer

28

Anode process gas supply

30

Anode process gas line

32

Hydrogen tank

34

Anode exhaust gas line

36

Return line

38

Valve

40

Valve

42

Cathode process gas supply

44

Cathode process gas line

46

air funding

48

Cathode exhaust gas line

50

lighting device

52

stack

54

with respect to the humidifying effect active area

56

border area

60

water vapor permeable membrane

70

first layer arrangement / dry layer arrangement

72

first flow layer

74

flow webs

76

flow channels

78

Spacer film

80

second layer arrangement / wet layer arrangement

82

second flow layer

84

flow webs

86

flow channels

88

stabilization point

90

Backing / supporting film

92

openings

94

adhesive layer

96

adhesive layer

98

end

100

Web height reduction

102

support point

104

holder cartridge

106

endplate

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 98/45889 A1 [0004]
• DE 102005025914 A [0005]
• US 2008/0241636 A1 [0007]
• DE 102008016087 A1 [0007]
• DE 102009005685 A1 [0008]
• US 2009/0092863 A [0009]
• DE 102008050507 A1 [0009]
• WO 2009/101036 A1 [0010]
• US 2008/0001313 A1 [0011]
• DE 102010035359 A1 [0011]

Claims (10)

Humidifying device ( 50 ) for humidifying process gases, in particular for fuel cells ( 12 ) comprising a stack ( 52 ) of repeating components comprising a) a water vapor permeable membrane ( 60 ), b) one, on a first side of the membrane ( 60 ) arranged first layer arrangement ( 70 ), comprising a first flow layer ( 72 ) for conducting a process gas to be humidified, a plurality of parallel to the membrane ( 60 ) running flow webs ( 74 ), which flow channels ( 76 ), and c) one, on a second side of the membrane ( 60 ) arranged second layer arrangement ( 80 ), comprising a second flow layer ( 82 ) for conducting a wet gas, which is a plurality parallel to the membrane ( 60 ) running flow webs ( 84 ), which flow channels ( 86 ), characterized in that at least a part of the flow webs ( 84 ) of the second flow layer ( 80 ) with a plurality of stabilization sites ( 88 ) in the form of local enlargements of the web widths (B) with respect to a parallel to the membrane ( 60 ) extending level are formed. Humidifying device ( 50 ) according to claim 1, characterized in that the flow webs ( 84 ) of the second flow layer ( 80 ) Web widths (B) outside the stabilization sites ( 88 ) of not more than 1.0 mm, in particular not more than 0.6 mm, preferably not more than 0.4 mm. Humidifying device ( 50 ) according to claim 1 or 2, characterized in that the flow webs ( 84 ) of the second flow layer ( 80 ) at their end sections ( 98 ) have larger web widths than at middle portions between the stabilization sites ( 88 ). Humidifying device ( 50 ) according to one of the preceding claims, characterized in that at least a part of the flow webs ( 84 ) of the second flow layer ( 80 ) local reductions ( 100 ) of the web height (H) with respect to an orthogonal to the membrane ( 60 ) level. Humidifying device ( 50 ) according to claim 4, characterized in that the local land height reductions ( 100 ) between the stabilization sites ( 88 ) are arranged. Humidifying device ( 50 ) according to one of the preceding claims, characterized in that the second layer arrangement ( 80 ) Furthermore, two, on both sides of the second flow layer ( 82 ) subsequent gas-permeable supporting layers ( 90 ) having. Humidifying device ( 50 ) according to claim 6, characterized in that the gas-permeable supporting layers ( 90 ) as support foils having a plurality of passage openings ( 92 ) are formed. Humidifying device ( 50 ) according to one of the preceding claims, characterized in that the first layer arrangement ( 70 ) Furthermore, two, on both sides of the first flow layer ( 72 ) adjoining spacer foils ( 78 ), which have a peripheral frame portion and at least one, bounded by the peripheral frame portion central recess. Humidifying device ( 50 ) according to one of the preceding claims, characterized in that the stack ( 52 ) of the repeating components is arranged in a housing, which is formed, the plurality of first flow layers ( 70 ) with a process gas supply ( 30 . 44 ) a fuel cell ( 12 ) and the plurality of second flow layers ( 82 ) with an exhaust gas discharge ( 34 . 48 ) a fuel cell ( 12 ) connect to. Fuel cell assembly ( 10 ) comprising a fuel cell stack ( 12 ) having a plurality of cathode portions and a plurality of anode portions, an anode process gas supply ( 28 ) and a cathode process gas supply ( 42 ), wherein the cathode process gas supply ( 42 ) and / or the anode process gas supply ( 28 ) a humidifying device ( 50 ) according to one of claims 1 to 9 for humidifying a cathode process gas or an anode process gas.

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