DE102019220534A1 - Electrochemical cell with a distribution plate - Google Patents

Abstract

The present invention relates to a distributor plate (7, 8), in particular for an electrochemical cell (1), the distributor plate (7, 8) having channels (11) and adjoining webs (12). The undersides of the webs (12) form a contact surface (13) of the distributor plate (7, 8). The contact surface (13) has at least partially a structure (30).

Description

The present invention relates to an electrochemical cell with a distribution plate and a corresponding distribution plate

State of the art

Distribution plates are known from the prior art. So is from the DE 10 221 951 B4 a distributor plate or bipolar plate for a fuel cell is known. The known distribution plate has channels and adjacent webs. The undersides of the webs form a contact surface between the distributor plate and a diffusion layer of the fuel cell. Accordingly, fuel cells with such distributor plates and underlying diffusion layers are also known.

The areas of the diffusion layers that run under the webs are comparatively poorly supplied with reaction gas, especially under flooding conditions, which can lead to an undesired inhomogeneous current density distribution.

Disclosure of the invention

In contrast, a fuel cell according to the invention or electrochemical cell with a distributor plate according to the invention has a significantly more homogeneous gas distribution, which preferably also leads to a more homogeneous current density distribution.

For this purpose, the distribution plate includes channels and adjacent webs. The undersides of the webs form a contact surface of the distributor plate. The contact surface is at least partially structured.

An electrochemical cell, in particular a fuel cell, with such a distributor plate also has a diffusion layer and an electrolyte; The electrolyte is preferably a membrane which is coated on both sides with electrodes. The undersides of the webs then form a contact surface between the distributor plate and the diffusion layer.

The structuring significantly improves the uniform supply of reaction gas to the diffusion layer under the contact surface, to the extent that the electrolyte or the electrode layer under the diffusion layer is homogeneously supplied with reaction gas over its entire surface. The structuring ensures that the additional convective and diffusive flows of the reaction gas or the reactant in the structuring transport more reaction gas into the diffusion layer under the webs. The gas supply under the webs, which is improved as a result, preferably also leads to a lower accumulation of condensed water precisely under these webs, in particular on a cathode side or in a cathode compartment of the fuel cell. Thus, the invention not only homogenizes the gas supply, but also the water discharge. This leads to an improved heat distribution and less aging of the electrochemical cell or the fuel cell. Because the structuring is introduced into the contact area, the illustrated increase in efficiency of the electrochemical cell is also achieved without increasing the installation space.

In an advantageous development, at least some of the channels have damming edges in their flanks in the area of the structuring. The channels define a main flow direction of the corresponding reaction gas of an electrochemical cell. The baffle edges now advantageously improve the diversion of part of the mass flow of the reaction gas from the channel into the structuring, i.e. from the main flow direction into a secondary flow direction, by damming up or deflecting part of the reaction gas, so that even more reaction gas is also under the webs in the diffusion layer and can flow or diffuse further to the electrode layers.

In preferred developments, one or more channels have offsets with respect to the damming edges along a flank. These offsets mean that the flank of the channel between two dam edges has an offset angle to the main flow direction. Viewed macroscopically, however, the channel has an essentially constant flow cross-section or an essentially constant channel width over its entire length. An offset angle to the main flow direction between two successive dam edges is advantageously 1 ° to 30 °.

The structuring advantageously connects two adjacent channels fluidically. This results in comparatively low flow losses within the structure, in particular if the connection is made at an advantageous angle of 45 ° to 60 ° to the main flow direction.

In preferred embodiments, the distributor plate has a coating in the contact surface. The coating can serve both to protect the distributor plate from corrosion and to reduce the electrical contact resistance to the diffusion layer. The structuring can be introduced into the coating, or into a base plate of the distributor plate to which the coating is applied, the Structuring is largely retained by the coating. In particular when the coating is applied additively, it is advantageous to apply the structuring only with the coating, since no additional manufacturing step is required for the structuring.

In advantageous embodiments, the structuring includes secondary channels. The cross section of a secondary channel is preferably smaller by at least a factor of 50 than the cross section of a channel. As a result, the channel carries a significantly higher mass flow of reaction gas in the main flow direction than a secondary channel, so that a sufficient supply of the diffusion layer with reaction gas is maintained under the channel.

The secondary channels are advantageously trapezoidal, wave-shaped, parallel, cross-shaped or honeycomb-shaped. This allows the flow of the reaction gas in the structuring and thus also in the underlying diffusion layers to be influenced in a targeted manner.

In designs of the distributor plate with secondary channels and retaining edges, it is particularly advantageous if the retaining edges are arranged flush at the entrance of the secondary channels. As a result, the reaction gas is slowed down in the main flow direction at the dam edges and introduced into the secondary channels. The supply of the secondary channels with reaction gas is particularly well designed as a result.

The invention also comprises an electrochemical cell, in particular a fuel cell, with a distributor plate according to the described embodiments. The electrochemical cell also has a diffusion layer and an electrolyte, which can be a membrane, for example, which in turn is coated with electrodes. The undersides of the webs of the distributor plate form the contact surface between the distributor plate and the diffusion layer.

In preferred developments, the diffusion layer is a fleece, particularly preferably a carbon fiber fleece. In the case of the fleece, the gas permeability in the direction of the thickness, ie in the direction of the electrolyte or the membrane, is comparable to the gas permeability in the plane direction, ie in the direction from “under the channels to under the webs”. The supply of the areas of the diffusion layer under the webs with reaction gas is therefore improved by the fleece in combination with the structuring of the contact surface. The present invention is particularly well suited for such nonwovens because the areas “under the webs” are supplied with reaction gas precisely by the structuring of the web itself and thus potential water accumulations “under the webs” can also be easily removed.

In advantageous embodiments, the electrochemical cell is a fuel cell or an electrolyzer, the electrolyte preferably being a coated polymer electrolyte membrane. An electrolyzer is a stationary energy converter which, when an electrical voltage is applied, preferentially splits hydrogen and oxygen from water. For the efficiency of a fuel cell or an electrolyzer with a polymer electrolyte membrane, it is particularly important to homogeneously supply the electrode layers arranged on the membrane with reaction gas.

The invention additionally comprises a motor vehicle which has a fuel cell stack with one or more of the described fuel cells according to the invention. The motor vehicle thus has a very efficient fuel cell or a fuel cell stack with many very efficient individual fuel cells. In mobile applications in particular, it is very important to achieve such increases in efficiency without increasing the installation space required for this.

• 1 schematisch eine aus dem Stand der Technik bekannte elektrochemische Zelle.
• 2 eine Wiederholeinheit einer Kanal-Steg-Struktur einer erfindungsgemäßen Verteilerplatte für eine elektrochemische Zelle in perspektivischer Ansicht auf einen Steg, wobei nur die wesentlichen Bereiche dargestellt sind.
• 3 einen Schnitt durch einen Bereich einer erfindungsgemäßen elektrochemischen Zelle, wobei nur die wesentlichen Bereiche dargestellt sind.
• 4 eine weitere erfindungsgemäße Verteilerplatte für eine elektrochemische Zelle in perspektivischer Ansicht, wobei nur die wesentlichen Bereiche dargestellt sind.
• 5 eine Draufsicht auf eine erfindungsgemäße Verteilerplatte, wobei nur die wesentlichen Bereiche dargestellt sind.
• 6 schematisch weitere Ausführungsformen eines strukturierten Stegs einer Verteilerplatte.

Embodiments of the invention are shown in the drawing and explained in more detail in the description below. It shows:

• 1 schematically an electrochemical cell known from the prior art.
• 2 a repeating unit of a channel-web structure of a distributor plate according to the invention for an electrochemical cell in a perspective view of a web, only the essential areas being shown.
• 3 a section through a region of an electrochemical cell according to the invention, only the essential regions being shown.
• 4th a further distribution plate according to the invention for an electrochemical cell in a perspective view, only the essential areas being shown.
• 5 a plan view of a distributor plate according to the invention, only the essential areas are shown.
• 6th schematically further embodiments of a structured web of a distributor plate.

1 shows schematically an electrochemical cell known from the prior art 1 in the form of a fuel cell, only the essential areas are shown. The fuel cell 1 has an electrolyte 2 , for example a membrane, in particular a polymer electrolyte membrane. To one side of the membrane 2 is a cathode room 1a , on the other side an anode compartment 1b educated.

In the cathode room 1a are from the membrane 2 pointing outwards - i.e. in the normal direction z - an electrode layer 3 , a diffusion layer 5 and a distribution plate 7th arranged. Analog are in the anode compartment 1b from the membrane 2 an electrode layer facing outwards 4th , a diffusion layer 6th and a distribution plate 8th arranged.

The distribution plates 7th , 8th assign channels 11 for the gas supply - for example air in the cathode compartment 1a and hydrogen in the anode compartment 1b -to the diffusion layers 5 , 6th on. The diffusion layers 5 , 6th typically exist on the duct side - i.e. to the distributor plates 7th , 8th out - from a carbon fiber fleece and on the electrode side - i.e. to the electrode layers 3 , 4th out - from a microporous particle layer.

The distribution plates 7th , 8th assign the channels 11 and thus implicitly also to the channels 11 adjacent walkways 12th on. The undersides of these webs 12th consequently form a contact surface 13th the respective distributor plate 7th , 8th to the underlying diffusion layer 5 , 6th .

According to the invention, the contact surface now has 13th at least partially a structuring 30th on. To do this shows 2 a section of a distribution plate 7th , 8th in a perspective view of a bridge 12th ; the cutout comprises, as it were, a repeating unit of a channel-web structure, with channels arranged alternately 11 and bars 12th as they are arranged, for example, over active surfaces of fuel cells. The distribution plate 7th , 8th shows a channel 11 for the gas supply to the diffusion layer, not shown, and a web 12th as known from the prior art. Also one from the canal 11 fluidically separated coolant channel 21 is known from the prior art.

In the canals 11 Usually, a reaction gas or a reactant of the electrochemical cell flows 1 , for example hydrogen or oxygen, in a main flow direction 11a which by the geometry of the channels 11 is given. The structuring 30th consists of secondary channels 31 , which in the execution of the 2 are designed in a zigzag shape or trapezoidal shape, two parallel side-by-side channels 11 connect fluidically and a secondary flow direction 31a set for the reactant. The cross-section of the secondary channels is preferred 31 significantly smaller than the cross-section of the channels 11 , particularly preferably at least by the factor 50 smaller. The trapezoidal alignment of the secondary channels 31 ensures that they are evenly spaced from the two adjacent canals 11 can be supplied with reaction gas.

The structuring 30th or the secondary channels 31 preferably have a depth T of 5 μm to 200 μm, more preferably 20 μm to 100 μm and particularly preferably 30 μm to 70 μm. The length L of the structure 30th or the secondary channels 31 can cover the entire width of a web 12th lead so that two adjacent channels 11 connected as in 2 shown; the gas flow in the secondary channels 31 is therefore comparatively strong. Alternatively, the length L can also be less than the width of the web 12th be so that the corresponding secondary channels 31 no connection between two adjacent channels 11 represent. The width B of the structure 30th or the secondary channels 31 is in the range from 10 µm to 1000 µm, preferably 50 µm to 200 µm.

The secondary channels 31 or the secondary flow direction 31a run at an angle α to the channels 11 or to the main flow direction 11a . The angle α is advantageously in the range from 0 ° to 90 °, preferably 30 ° to 75 °, and particularly preferably 45 ° to 60 °.

In addition to the exemplary embodiment of the zigzag shape of the structuring 30th other designs are conceivable. Examples of this are secondary channels 31 as curved lines, as exclusively parallel lines, as intersecting lines or as lines that form a honeycomb-like grid. Combinations of these designs are of course also conceivable.

In these exemplary embodiments, the reactant or the gas can therefore be in the secondary channels 31 between two channels 11 move. This happens automatically due to the strong convective flow. According to the invention, this creates the area of the diffusion layers 5 , 6th under the bridges 12th better supplied with reaction gas. The homogeneity of the gas supply to the electrolyte 2 or to the electrode layers 3 , 4th in normal direction z is improved. The homogeneity of the gas supply in the xy plane of the gas supply to the electrolyte results in the homogeneity of the gas supply 2 or to the electrode layers 3 , 4th understood, the gas supply to the electrolyte 2 takes place mainly in the normal direction z.

Due to the additional convective flows of the reactants in the side channels 31 effectively gets more gas into the diffusion layers 5 , 6th under the bridges 12th transported. The resulting improved gas supply under the bars 12th also leads to a lower accumulation of condensed water precisely under these webs 12th , because the gas flow for better water discharge under the webs 12th cares. Not only the gas supply is thus homogenized, but also the water discharge, especially when the distributor plate according to the invention 7th in the cathode compartment 1a a fuel cell is arranged.

The structuring 30th can advantageously, for example, directly into the distributor plate by means of embossing 7th , 8th be introduced. However, it can also be equivalent to this by means of material removal - for example laser structuring or etching - or by means of a coating 15th the contact area 13th be generated. To do this shows 3 a section through a region of an electrochemical cell 1 , whereby only the essential areas are shown. The distribution plate 7th , 8th points in this version in the contact area 13th a coating 15th with a coating thickness b, the coating 15th preferably the electrical conductivity between the distributor plate 7th , 8th and the underlying diffusion layer 5 , 6th improved. In alternative designs, the flanks of the webs 12th showing the channels 11 limit with the coating 15th be provided.

The structuring 30th , which in the representation of the 3 cannot be seen, can now be done by means of a varying layer thickness of the coating 15th can be generated, especially if the coating is applied by means of an additive manufacturing process. As an alternative or in addition to this, the one under the coating can also be used 15th lying base plate 7a , 8a the distribution plate 7th , 8th already an analogous structure 30th have, which then through the coating 15th is largely retained with a constant layer thickness. The base plate 7a , 8a represents the original, mostly metallic, semi-finished product of the distributor plate 7th , 8th but without coating 15th represent.

The depth T of the structure 30th can through the coating 15th advantageously up to 200 μm thick, but preferably 10 μm to 100 μm and particularly preferably 20 μm to 70 μm thick. The coating 15th is preferably carbon-based, advantageously made of carbon particles with a binder - for example made of carbon black with a binder or graphite with a binder.

Assigns the distribution plate 7th , 8th both a structuring 30th as well as a coating 15th on, the following ratios are advantageous: The structuring 30th or the secondary channels 31 have a preferred depth T of 0.2-1.0 times the coating thickness b, particularly preferably 0.7-1.0 times the coating thickness b.

3 also shows an example of a duct measuring point M1 and a land measurement point M2 . The channel measuring point M1 is in a channel 11 arranged, preferably on the cathode side of a fuel cell; in this case it is an example of an area in the channel through which the oxidizing agent flows well 11 . The land measuring point M2 is in the diffusion layer 5 , 6th or between the diffusion layer 5 , 6th and the distribution plate 7th , 8th under the jetty 12th arranged, preferably also on the cathode side of the fuel cell; it is also an example of a region in the diffusion layer through which the oxidizing agent flows rather poorly 5 , 6th .

Simulations now show for the duct measuring point M1 when he is close to a cathode outlet of the duct 11 is an oxygen concentration of 11%. In the case of an unstructured contact area 13th results in the simulation for the land measuring point M2 an oxygen concentration of 2.4%; in the case of a structured contact surface 13th however results for the land measuring point M2 an oxygen concentration of 4.7%. The supply of the underlying electrode layer with oxidizing agent can thus be significantly improved according to the simulation. The simulation was structured 30th based on how they are essentially in the 2 is shown, with a depth T of 100 µm. For this simulation result, it is irrelevant whether the contact surface 13th a coating 15th has or not.

4th shows an embodiment similar to 2 . In the further training of the 4th assign the channels 11 in the area of structuring 30th however, there are additional damming edges in their flanks 35 on. The jam edges 35 can advantageously be in the flanks of the channels 11 quasi continuations of the structuring 30th represent.

• - unter den Stegen 12 um 70% erhöht werden.

Through the jam edges 35 becomes that in the main flow direction 11a flowing gas or fluid effectively in the secondary channels 31 the structuring 30th directed. In the execution of the 4th form the jam edges 35 staggered structures, which for example in the distributor plate 7th , 8th can be imprinted; the jam edges 35 can also be applied by removal or additive coatings. The jam edges 35 lead to a significantly increased flow of the reactants into the structuring 30th , so in the secondary channels 31 . The diffusion of the reactant into the areas of the diffusion layer 5 , 6th , which in the normal direction z under the webs 12th is significantly improved. The stowage edges are preferred for this purpose 35 flush with the entrance of the secondary channels 31 appropriate. In the first simulations, this enabled the minimum oxygen content in the cathodic diffusion layer 5 - in the interface to the electrode layer 3

• - under the bridges 12th can be increased by 70%.

5 shows a plan view of a web 12th a distribution plate 7th , 8th . This distribution plate 7th , 8th is a further development of the execution according to 4th . The flush at the entrance of the side channels 31 arranged storage edges 35 are easy to see. In the execution of the 5 the flanks of the channels have dislocations 36 with dislocation lengths V. The dislocations 36 are wedge-shaped under one Offset angle β to the main flow direction 11a arranged. Preference is given to the offset angle β, the offset length V and a damming edge depth D of the damming edges 35 chosen so that the width of the web 12th does not change over its length. The offset angle β is advantageously 1 ° to 30 ° and particularly preferably 1 ° to 10 °. The dislocation length V is advantageously 100 μm to 2000 μm and particularly preferably 200 μm to 1000 μm.

• - 6a) wellenförmige Anordnung der Nebenkanäle 31.
• - 6b) parallele Anordnung der Nebenkanäle 31.
• - 6c) kreuzförmige Anordnung der Nebenkanäle 31.
• - 6d) wabenförmige Anordnung der Nebenkanäle 31.

6th shows schematically further embodiments of the structuring 30th , whereby only the essential areas are shown. In addition to the trapezoidal arrangement of the secondary channels 31 like them in the 2 and 4th is shown show the 6 ad following designs:

• - 6a) undulating arrangement of the secondary channels 31 .
• - 6b) parallel arrangement of the secondary channels 31 .
• - 6c ) cross-shaped arrangement of the secondary channels 31 .
• - 6d ) honeycomb arrangement of the secondary channels 31 .

The trapezoidal, wave-shaped, cross-shaped and honeycomb arrangements of the secondary channels 31 have the advantage that the secondary channels 31 of both on the associated bridge 12th adjacent canals 11 can be fed with reaction gas. This enables a targeted, uniform flow of the reaction gas under the webs 12th in the diffusion layers 5 , 6th be forced.

In contrast to this, the parallel arrangement of the secondary channels works 31 a targeted inhomogeneous flow of the reaction gas in the secondary channels 31 from a canal 11 to the next. In this way, on the one hand, the flow losses can be reduced, on the other hand, the supply of the electrode layers can also be achieved 3 , 4th offset in the z-direction to the structure of the channels 11 respectively.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 10221951 B4 [0002]

Claims (16)

Distribution plate (7, 8), in particular for an electrochemical cell (1), the distribution plate (7, 8) having channels (11) and adjacent webs (12), the undersides of the webs (12) having a contact surface (13) of the Form distribution plate (7, 8), characterized in that the contact surface (13) at least partially has a structure (30). Distribution plate (7, 8) Claim 1 characterized in that at least some of the channels (11) have retaining edges (35) in their flanks in the area of the structuring (30). Distribution plate (7, 8) Claim 2 characterized in that the channel (11) has offsets (36) of the retaining edges (35) along one flank. Distribution plate (7, 8) after one of the Claims 1 to 3 characterized in that the structuring (30) fluidly connects two adjacent channels (11). Distribution plate (7, 8) after one of the Claims 1 to 4th characterized in that the distributor plate (7, 8) has a coating (15) in the contact surface (13). Distribution plate (7, 8) Claim 5 characterized in that the structuring (30) is introduced into the coating (15). Distribution plate (7, 8) Claim 5 characterized in that the structuring (30) is introduced into a base plate (7a, 8a) of the distributor plate (7, 8), the structuring (30) being largely retained by the coating (15). Distribution plate (7, 8) after one of the Claims 1 to 7th characterized in that the structuring (30) comprises secondary channels (31), the cross section of a secondary channel (31) preferably being at least 50 times smaller than the cross section of a channel (11). Distribution plate (7, 8) Claim 8 characterized in that at least some of the channels (11) have retaining edges (35) in their flanks in the area of the structure (30), the retaining edges (35) being arranged flush at the entrance of the secondary channels (31). Distribution plate (7, 8) Claim 8 or 9 characterized in that the secondary channels (31) are trapezoidal, cross-shaped or wave-shaped. Distribution plate (7, 8) Claim 8 or 9 characterized in that the secondary channels (31) are arranged in parallel. Distribution plate (7, 8) Claim 8 or 9 characterized in that the secondary channels (31) are arranged in a honeycomb shape. Electrochemical cell (1) with a distributor plate (7, 8) according to one of the preceding claims, wherein the electrochemical cell (1) has a diffusion layer (5, 6) and an electrolyte (2), the undersides of the webs (12) having a Form the contact surface (13) of the distributor plate (7, 8) with the diffusion layer (5, 6). Electrochemical cell (1) according to Claim 13 characterized in that the diffusion layer (5, 6) is a fleece, in particular a carbon fiber fleece. Electrochemical cell (1) according to one of the Claims 13 or 14th characterized in that the electrochemical cell (1) is a fuel cell or an electrolyzer, the electrolyte (2) preferably being a polymer electrolyte membrane. Motor vehicle with an electrochemical cell (1) designed as a fuel cell according to one of the Claims 13 to 15th .

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