DE102007048184B3 - Electrochemical system and biopolar plate - Google Patents

Abstract

The present invention describes an electrochemical system and a bipolar plate for use in an electrochemical system. The electrochemical system (1) consists of a layering of several cells (2) which are separated from each other by bipolar plates (3), wherein the bipolar plates openings for cooling (4) or for supply and removal (5) of operating media to the cells and at least one cell has an electrochemically active region (6) surrounded by a boundary wall (7) of the bipolar plate and within the electrochemically active region a channel structure (8) of the bipolar plate is provided for uniform media distribution , wherein at least one gas diffusion layer (9) is provided for micro distribution of medium. In the boundary region between the channel structure and the boundary wall delimiting elements (10) are provided to prevent the fluid from flowing past between channel structure and boundary wall, wherein the gas diffusion layer covers the channel structure and / or at least parts of the boundary elements. Preventing the "flown through" in the boundary region of the electrochemically active field, the reliability and efficiency of electrochemical systems is significantly increased.

Description

The The present invention relates to an electrochemical system as well a bipolar plate for use in such a system.

The Electrochemical system, for example, a fuel cell system or an electrochemical compressor system, in particular an electrolyzer in which by applying a potential next to the generation of hydrogen and oxygen from water these gases simultaneously be compressed under pressure. In addition, there are also electrochemical Compressor systems such. B. electrochemical hydrogen compressors known which gaseous molecular hydrogen is supplied and in which this by the application of a potential electrochemical is compressed. This electrochemical compression offers itself especially for small amounts of hydrogen to be compressed, as a mechanical Compression of hydrogen would be significantly more complex here.

• – Elektrische Kontaktierung der Elektroden der einzelnen elektrochemischen Zellen (z. B. Brennstoffzellen) und Weiterleitung des Stroms zur benachbarten Zelle (Serienschaltung der Zellen),
• – Versorgung der Zellen mit Medien, z. B. Reaktionsgasen, und Abtransport von Reaktionsprodukten über eine Kanalstruktur, die in einem elektrochemischen aktiven Bereich angeordnet ist (Gasverteilerstruktur/Flowfield),
• – Weiterleiten der bei der Erzeugung in der elektrochemischen Zelle entstehenden Abwärme, sowie
• – Abdichten der verschiedenen Medien- bzw. Kühlkanäle gegeneinander und nach außen.

There are electrochemical systems are known in which an electrochemical cell stack with a layering of several electrochemical cells, which are each separated by bipolar plates, are constructed. The bipolar plates have several tasks here:

• Electrical contacting of the electrodes of the individual electrochemical cells (eg fuel cells) and forwarding of the current to the neighboring cell (serial connection of the cells),
• - Supplying the cells with media, eg. B. Reaction gases, and removal of reaction products via a channel structure, which is arranged in an electrochemical active region (gas distribution structure / flowfield),
• - Forwarding of the resulting in the generation in the electrochemical cell waste heat, as well
• - Sealing the different media or cooling channels against each other and to the outside.

For the media or removal from the bipolar plates to the actual electrochemical cells, these are z. B. MEA (Membrane Electrode Assembly, i.e. membrane electrode assembly) with a respective gas diffusion layer oriented towards the bipolar plates (For example, from a metal or carbon nonwoven), the Bipolar plate openings for cooling or media supply and removal.

at known bipolar plates, the gas distribution takes place along the MEA or the gas diffusion layer by means of channel and meander structures on both sides the bipolar plate.

It is known, especially in metallic bipolar plates, channel structures to memorize and Here also a boundary wall, the electrochemically active Area surrounds, equal to impress. The boundary wall has this often bead-shaped Shape. Now it has been determined in test series that such bipolar plates may show strong performance variations due to insufficient areal distribution attributed to media seem to be.

It is therefore the object of the present invention, an electrochemical System or to create a bipolar plate that is not due to insufficient distributions of media in the electrochemically active field power fluctuations demonstrate.

These Task is governed by the objects of independent claims solved.

This is first once an electrochemical system consisting of a stratification several cells, each separated by bipolar plates from each other are, with the bipolar plates openings for cooling or for delivery to and from the cells and stratification can be placed under mechanical compressive stress, wherein at least one Cell surrounded by a boundary wall of the bipolar plate having electrochemically active region and within the electrochemically active Area a channel structure of the bipolar plate for uniform media distribution is provided, wherein at least one gas diffusion layer for microdistribution is provided by medium. In the border area between the channel structure and the boundary wall limiting elements are provided for Avoiding the rush by of fluid between channel structure and boundary wall. This covers the gas diffusion layer the channel structure and / or at least parts the boundary elements.

The Bipolar plate for use in an electrochemical according to the invention System is characterized in that this bipolar plate is a ground plane has and out of this basic level outstanding a channel structure as well as openings to Media supply and removal are provided and the channel structure as well the openings from one (maybe with openings provided for media execution) Boundary wall are surrounded and that in the area between boundary wall and the outer edge the channel structure at least one limiting element to prevent of passing by of medium in the boundary between the boundary wall and channel structure is provided.

Thus, with the "limiting elements" according to the invention, bypassing of the medium at the channel structure is largely prevented. As a result, a uniform media distribution over the channel structure is achieved and in this way the unwanted Leistungsschwan excluded.

Especially It is advantageous if the gas diffusion layer not only the Channel structure, but also at least parts of the boundary elements covered. This leads to an additional Compression of the gas diffusion layer in this area, which is stronger as the compression in the area of the "normal" channel structure. Thus, a past by Medium in the area in question between channel structure and boundary wall so again stronger prevented.

advantageous Further developments of the present invention are described in the dependent claims.

A advantageous development provides that the height of the boundary elements chosen like that is that the compression of the gas diffusion layer in the contact area stronger to the delimiting elements is as in the touch area to the channel structure. This will be a very good seal achieved in this border area. Another advantageous development provides that the boundary elements are designed as extensions of the channel structure, which pass into the boundary walls. Especially with metallic bipolar plates this is very advantageous because thus a common coinage with the delimiting elements or elements of the channel structure is possible. In principle it is possible to enter or provide more limiting elements. For multiple boundary elements these are preferably spaced apart, and more preferably form here two adjacent boundary walls together with the boundary elements each chambers between channel structure and boundary wall, so that (as with a cargo ship) bulkheads are formed to bypass preferably safe to prevent.

Of the Repeating distance of individual boundary elements is in this case preferably greater than 2 mm, more preferably greater than 5-10 mm (at shorter distances would the Bead mechanically too much weakened). As an alternative differentiator it could also be said that on 100 mm length provide the boundary wall here at least one limiting element is, but preferably five to twenty-five Limiting elements. A further advantageous development sees before that the boundary wall is serpentine. In snake-shaped course of Boundary wall can each be close to the channel structure Section of the boundary wall with the channel structure over a Be connected limiting element.

For the delimiters, the "Bypass" between the boundary wall and channel structure, it is advantageous that these both substantially transverse to the boundary wall and substantially across to the extreme Run elements of the channel structure.

The Design of the limiting elements is also dependent on the respective execution the channel structures. For example, if the channel structures are as Single elements provided, so can the limiting elements also be provided in a line, so to here to prevent a "bypass". Otherwise, These limiting elements should also be provided as individual elements.

A Another advantageous embodiment provides that the boundary wall across from a ground plane of the bipolar plate has a greater height than the vast majority increase the channel structure in the vicinity of the boundary wall with respect to this Ground plane. With "Nahbereich" here is a Distance from the boundary wall of a maximum of 1 cm to understand.

The Limiting elements should be from the ground plane of the bipolar plate at least the height of the vast majority Have survey of the channel structure. This means that they are so preferably in height equal or between the height the canal structure and the height the boundary wall should be.

The Limiting elements are preferably embossed in a (preferably metallic) bipolar plate provided.

A Another advantageous embodiment provides that a bipolar plate is constructed of two plates, wherein the at least one limiting element on the side facing away from the electrochemically active side hollow is and this cavity as a complementary space for plugging the second plate of the bipolar plate is provided.

The boundary walls preferably have the shape of a bead, in particular a full bead or a half bead and are thus an integral part of the bipolar plate, however, attachments are also possible here.

A Particularly advantageous embodiment provides that the openings the bipolar plate for cooling or removal and supply of media with elastic bead arrangements are provided, said bead assemblies breakthroughs for Passage of liquid or gaseous Media in a cavity of the bipolar plate or the electrochemical active area.

Preferably, the conduction of media through the electrochemically active region is such the point of introduction of the medium and the point of discharge of the medium take place at respectively maximally distant points of the electrochemically active region. As a result, the basic prerequisite is created to achieve the largest possible distribution, this is also a meandering guide makes sense, even if dead-end versions are also possible. In such cases, however, a flow resistance within the electrochemically active region must always be overcome so that the medium always seeks "short cuts" or "bypasses". Therefore, the present invention with the limiting elements is particularly useful here.

Further Advantageous developments of the present invention are shown in FIG the rest dependent claims specified.

The Invention will now be explained with reference to several figures. Show it:

1a to 1c the construction of a fuel cell stack,

2a and 2 B Top views of differently designed bipolar plates,

3a and 3b Cross sections through a bipolar plate arrangement according to the invention ( 3a ) or a bipolar plate arrangement according to the prior art ( 3b )

4 the cathode-side profile of volume flow via dynamic pressure with or without delimiting elements,

5 a plan view with respect to another embodiment of a bipolar plate with limiting elements,

6 a representation of a centering according to BB 5 .

7 Flow resistance curves of inventive electrochemical systems at different pressures.

1a to 1c show the basic structure of an electrochemical system in the form of a fuel cell stack (fuel cell stack) 1 , This has a layering of several fuel cell arrangements 12 on (see 1b ). The stratification of these fuel cell arrangements 12 is held together by end plates, which z. B. over clamping bolts, as in 1c shown to apply a compressive stress on the stratification of the fuel cell assemblies.

The following is the construction of a fuel cell assembly 12 discussed in more detail.

1a shows the internal structure of a fuel cell assembly 12 in the form of an exploded drawing. This is initially a cell (for example fuel cell) 2 comprising an ion-conductive polymer membrane, at least in an electrochemically active region 6 provided with a catalyst layer on both sides. In the fuel cell assembly 12 are also two bipolar plates 3 provided between which the fuel cell 2 is arranged. In the area between each bipolar plate and the nearest fuel cell 2 is also a gas diffusion layer 9 arranged. A surround, not shown, substantially in the edge region of the bipolar plates surrounding bead forms a boundary wall and thus ensures a seal of the electrochemically active region 6 , so that no coolant or media can escape from this area to the outside or vice versa.

In addition, the bipolar plates contain 3 aligned openings ("interface channels"). This is on the one hand an opening 4 for passing coolant, this opening 4 is surrounded by another bead arrangement. There is also an opening 5 for media supply and removal in the electrochemically active area 6 provided, which is bounded by a further bead arrangement. There are also transit openings for in 1a Verspannbolzen not shown provided.

2a shows a plan view of a portion of a bipolar plate according to the invention. You can see here an opening for media supply and removal 5 which is surrounded by a circular full bead. This full bead or bead arrangement has openings for the passage of liquid or gaseous media into a cavity of the bipolar plate or to the electrochemically active region. The bipolar plate shown 3 is made of metal, with the channel structure 8th or the boundary wall 7 are executed as imprints.

In 2a is shown here for clarity only the upper left corner of the bipolar plate. The conduction of media through the electrochemically active area 6 However, this is done in such a way that the point of introduction of the medium and the point of discharge of the medium at each of the most distant points of the electrochemically active region, preferably at the surface diagonals of the surface plane, as in 2a is shown.

The course of the boundary wall 7 is in 2a shown serpentine, at least in the 2a top right section shown.

It is also shown that in snakes shaped course of the boundary wall 7 one to the channel structure 8th Hin close lying section of the boundary wall with the channel structure via a limiting element 10 connected is.

Here is also removable, that the limiting element 10 essentially to the boundary wall 7 transversely or substantially transversely to the boundary wall 7 next (outermost) elements of the channel structure 8th ,

Besides, it is off 2a removable, that the limiting element 10 as an extension of the channel structure 8th is executed, which in the boundary wall 7 passes.

2 B shows an alternative embodiment of the in 2a shown bipolar plate.

Unlike the in 2a shown bipolar plate here are several limiting elements 10 intended. These are spaced apart, so that two adjacent boundary elements 10 each chambers between the channel structure 8th (ie the outermost element of the channel structure) and the boundary wall 7 form.

Of the Repeating distance of individual boundary elements is in this case preferably greater than 2 mm, more preferably greater than 5-10 mm.

So it is obvious that in the 2a respectively. 2 B shown embodiments limiting elements 10 are provided which a "bypass" (ie, a "pass by") of medium between the boundary wall 7 and the outermost elements of the channel structure 8th prevent. This is in 2a executed as a single crosspiece, in 2 B as a plurality of transverse webs, which then form corresponding chambers. It is important that these delimiters 10 perform this function, so they are not designed as lead-in beads or feeds to cooling or media channels.

In this way, the flow of medium, for example, from the media supply port 5 emanating, through the meandering running channel structure 8th forced, this is reflected in an increased dynamic pressure, which thus also provides an indicator of higher reaction rates of media in the fuel cell.

3a shows a cross-sectional view of a structure, the two bipolar plates 3 (for example according to 2a respectively. 2 B ) shows. Here is a fuel cell or a polymer electrolyte membrane (PEM) 2 between two bipolar plates 3 arranged. In the electrochemically active area is also on each side of the PEM 2 a gas diffusion layer 9 arranged. This gas diffusion layer can be prefabricated and designed as an immediate part of a membrane-electrode assembly, and the gas diffusion layers can be provided as separate layers.

It is essential that the height of the delimiting elements 10 is chosen such that the compression of the gas diffusion layer 9 in the area of contact with the boundary elements 10 is stronger than in the contact area to the channel structure 8th , This will be in 3a indicated by the closer hatching and drawing.

Also it can be seen that the boundary wall 7 opposite a ground plane 11 the bipolar plate 3 has a greater height than the predominant increase in the channel structure relative to this ground plane (this is indicated by the double arrows in FIG 3a displayed). It can also be seen that the boundary elements 10 starting from this ground plane 11 the bipolar plate 3 at least the height of the highest elevation of the canal structure 8th but not more than the height of the boundary wall 7 opposite the ground plane (this too is on the double arrows in 3a visible).

3b in contrast shows an arrangement which has no boundary elements and in which an additional compression of the gas diffusion layer in the outer edge region is not given.

The previously referenced figures, in particular the 1a to 1c . 2a . 2 B such as 3a , so show a bipolar plate 3 , where this is a ground plane 11 has and out of this basic level outstanding a channel structure 8th as well as openings 5 are provided for media supply and removal and the channel structure and the openings of a boundary wall 7 are surrounded and at least one boundary element in the region between the boundary wall and the outer edge of the channel structure 10 to prevent the medium from flowing past in the boundary area between the boundary wall 7 and channel structure 8th is to provide.

Shown is thus in the aforementioned figures, an electrochemical system 1 consisting of a layering several cells 2 , each by bipolar plates 3 are separated from each other, wherein the bipolar plates openings for cooling 4 or for delivery and delivery 5 from operating media to the cells and the stratification is settable under mechanical compressive stress, wherein at least one cell is one of a boundary wall 7 The bipolar plate surrounded electrochemically active area 6 and within the electrochemically active region a channel structure 8th the bipolar plate is provided for uniform media distribution, wherein at least one gas diffusion layer 9 is provided for micro-distribution of medium and in the boundary region between the channel structure and the boundary wall boundary elements 10 are provided to avoid the Vorbeiströmens of fluid between the channel structure and the boundary wall in the electrochemically active area (ie not in the cooling area) and the gas diffusion layer, the channel structure and / or covers at least parts of the boundary elements. Because of this covering so "jamming" or increased compression of the gas diffusion layer is achieved in the edge region, and this results in an even better seal, since not only the height of the boundary wall, but also the compression of the gas diffusion layer in this area for preventing the Bypasses (passing) provides.

4 shows the course of a volume flow in liters per minute over the back pressure in millibars, as it represents for an electrochemical system.

The left-hand curve shows a conventional design on the cathode side (for example, with a cross-section according to FIG 3b ), in which a flow-through of medium at the gas diffusion layer is possible. The right-hand curve shows a compression with limiting elements, so that a bypass is thereby prevented or limited. It can be seen here that at the same volume flow a much higher dynamic pressure is present, this is an indication that the medium is not simply "flowing past" without being led through the electrochemically active field. As a result, a constant reaction is forced, since the reaction medium no longer "spills past" unused.

5 shows a further embodiment of a bipolar plate according to the invention. Here are from a boundary wall 7 surrounded electrochemically active area 6 channel structures 8th provided, but are designed mainly as disjoint, so individual surveys. This is again a bipolar plate with a flowfield (electrochemically active region) in which the reaction medium from the top left is diagonally downwards to the right (exit there 5 ). In two places (bottom left and top right) are boundary elements 10 provided, which prevent an unwanted "bypass".

6 shows a cross section according to BB of the plate assembly 5 on an enlarged scale. Here it can be seen that there is a bipolar plate is composed of two plates, wherein the at least one limiting element 10 on the side facing away from the electrochemically active side is hollow and this cavity is provided as a complementary space for inserting the second plate of the bipolar plate. In this way, a centering of both Plat is also made th, so that the dimensional accuracy of the overall plate is thereby increased.

7 shows (similar to the above in 4 shown) the volume flow of (dry) air in liters per minute above the back pressure (in millibars). It can also be seen that with increasing pressure values in the overall composite (see 1c ) At a respective same volume flow of air, a significantly higher back pressure arises and that uniformly reproducible values can be set in this way.

Claims (20)

Electrochemical system ( 1 ), consisting of a layering of several cells ( 2 ), each by bipolar plates ( 3 ) are separated from each other, wherein the bipolar plates openings for cooling ( 4 ) or for the removal and supply of operating media ( 5 ) to the cells and the layering is settable under mechanical compressive stress, wherein at least one cell from a boundary wall ( 7 ) of the bipolar plate surrounded electrochemically active region ( 6 ) and within the electrochemically active region a channel structure ( 8th ) of the bipolar plate is provided for uniform media distribution, wherein at least one gas diffusion layer ( 9 ) is provided for micro-distribution of medium, characterized in that in the boundary region between the channel structure and the boundary wall boundary elements ( 10 ) are provided to avoid the flow past fluid between the channel structure and the boundary wall and the gas diffusion layer, the channel structure and / or at least parts of the boundary elements covered. System according to claim 1, characterized in that the height of the boundary elements ( 10 ) is selected such that the compression of the gas diffusion layer ( 9 ) in the area of contact with the limiting elements ( 10 ) is stronger than in the area of contact with the channel structure ( 8th ). System according to one of the preceding claims, characterized in that the limiting elements ( 10 ) are designed as extensions of the channel structure, which pass into the boundary walls. System according to one of the preceding claims, characterized in that one or more limiting elements ( 10 ) are provided. System according to claim 4, characterized in that individual limiting elements ( 10 ) are spaced apart, so that two neigh limited boundary elements ( 10 ) each chambers between the channel structure and the boundary wall ( 7 ). System according to one of claims 4 or 5, characterized in that the repetition distance of individual boundary elements ( 10 ) is greater than 2 mm, preferably greater than 5 to 10 mm. System according to one of the preceding claims, characterized in that the boundary wall ( 7 ) runs serpentine. System according to claim 7, characterized in that with serpentine course of the boundary wall ( 7 ) each to the channel structure ( 8th ) adjacent portion of the boundary wall with the channel structure via a limiting element ( 10 ) connected is. System according to one of the preceding claims, characterized in that the limiting elements ( 10 ) extend substantially transversely to the boundary wall. System according to one of the preceding claims, characterized in that the limiting elements ( 10 ) substantially transversely to the outermost elements of the channel structure ( 8th ). System according to one of the preceding claims, characterized in that when the channel structures ( 8th ) as individual elements the boundary elements ( 10 ) or in the form of individual elements. System according to one of the preceding claims, characterized in that the boundary wall ( 7 ) in relation to a ground plane ( 11 ) of the bipolar plate ( 3 ) has a greater height than the highest increase of the channel structure in the adjacent vicinity of the boundary wall with respect to this ground plane. System according to one of the preceding claims, characterized in that the limiting elements ( 10 ) starting from a ground plane ( 11 ) of the bipolar plate at least the height of the predominant elevation of the channel structure ( 8th ) exhibit. System according to one of the preceding claims, characterized in that the limiting elements ( 10 ) as impressions in a bipolar plate ( 3 ) are executed. System according to one of the preceding claims, characterized in that a bipolar plate ( 3 ) is composed of two plates, wherein the at least one limiting element ( 10 ) Is hollow on the side facing away from the electrochemically active side and this cavity is provided as a complementary mental space for inserting the second plate of the bipolar plate. System according to one of the preceding claims, characterized in that the boundary wall ( 7 ) has the shape of a bead, in particular a full bead or a half bead. System according to one of the preceding claims, characterized in that the bipolar plate ( 3 ) consists of metal. System according to one of the preceding claims, characterized in that the openings of the bipolar plate for cooling ( 4 ) or supply and delivery ( 5 ) are provided by media with elastic bead assemblies, said bead assemblies have openings for the passage of liquid or gaseous media in a cavity of the bipolar plate or the electrochemically active region out. System according to one of the preceding claims, characterized in that the conduction of media through the electrochemically active region ( 6 ) takes place in such a way that the point of introduction of the medium and the point of discharge of the medium take place at respectively maximally distant points of the electrochemically active region. Bipolar plate for use in an electrochemical system according to any one of the preceding claims, characterized in that it comprises a ground plane ( 11 ) and from this ground plane outstanding a channel structure ( 8th ) and openings ( 5 ) to the media supply and removal and the channel structure and the Publ openings of a boundary wall ( 7 ) are surrounded and that in the region between the boundary wall and the outer edge of the channel structure at least one boundary element ( 10 ) is provided to prevent the flow past medium in the boundary region between the boundary wall ( 7 ) and channel structure.