CN111463448A

CN111463448A - Gas distributor structure for fuel cell and electrolyzer

Info

Publication number: CN111463448A
Application number: CN202010053118.6A
Authority: CN
Inventors: U·贝尔纳
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-01-18
Filing date: 2020-01-17
Publication date: 2020-07-28
Also published as: DE102019200617A1

Abstract

The invention relates to a gas distributor structure (14) for a fuel cell or electrolyser, in particular a PEM fuel cell (10), having a fabric (80) for distributing reactants, wherein the fabric (80) has at least two fibers (81, 82, 83) that differ from one another. The at least two mutually different fibers (81, 82, 83) of the fabric (80) are embodied as threads (90, 92) of a carrier material (104, 106) extending in the vertical direction or in the horizontal direction, which carrier material is provided with a coating (100) or a multi-layer coating (113) of a functional material (108, 110, 112).

Description

Gas distributor structure for fuel cell and electrolyzer

Technical Field

The present invention relates to a gas distributor structure particularly suitable for fuel cells and electrolysers and to the use thereof.

Background

A fuel cell is a primary cell that converts the chemical reaction energy of a continuously supplied fuel and an oxidant into electrical energy. Thus, a fuel cell is an electrochemical transducer. In the known fuel cell, hydrogen (H) is used in particular₂) And oxygen (O)₂) Conversion to water (H)₂O), electrical energy, and heat. Electric powerThe electrolysis device is an electrochemical transducer which uses electrical energy to electrolyze water (H)₂O) to hydrogen (H)₂) And oxygen (O)₂)。

Furthermore, Proton Exchange Membrane (PEM) fuel cells are known. Also known are anion exchange membranes for use in both fuel cells and electrolysers. Proton exchange membrane fuel cells have a centrally arranged membrane which is conductive for protons, i.e. for hydrogen ions. The oxidizing agent, in particular oxygen in air, is thereby spatially separated from the fuel, in particular hydrogen.

The proton exchange membrane-fuel cell also has an anode and a cathode. Fuel is supplied at the anode of the fuel cell and catalytically oxidized to protons given electrons. The protons pass through the membrane to the cathode. The given electrons are conducted from the fuel cell and flow to the cathode via an external circuit. The oxidant is supplied at the cathode of the fuel cell and reacts to water by receiving electrons from an external circuit and protons that reach the cathode via the membrane. The water produced in this way is conducted away from the fuel cell. The total reaction is as follows:

O₂+4H⁺+4e^-→2H₂O

here, a voltage is applied between the anode and the cathode of the fuel cell. In order to increase the voltage, a plurality of fuel cells can be arranged mechanically one after the other in a fuel cell stack and electrically connected in series.

In order to distribute the fuel evenly to the anode and the oxidant evenly to the cathode, bipolar plates are provided. The bipolar plates have, for example, a channel-like structure for distributing the fuel and the oxidant to the electrodes. The channel-like structure also serves to conduct away the water produced during the reaction. The bipolar plate may also have structure for conducting cooling liquid through the fuel cell to conduct heat away.

A fuel cell having a bipolar plate, which is constructed from two plate halves, is known from DE 102012221730 a 1. In this case, each of the two plate halves has a distribution region which is provided for distributing the reaction gas.

DE 102014207594 a1 shows a bipolar plate for a fuel cell. The bipolar plate has meandering channels, which are embodied, for example, as grooves. The zigzag channel serves to introduce hydrogen or oxygen into the fuel cell.

Unlike PEM fuel cells which operate at operating temperatures of < 120 ℃, the electrolysers are not equipped with cooling channels. The stacked or repeating units of this configuration form a stack. Reactant H in air or water and in a cooling liquid₂And O₂Introduced into the cell by a media distributor structure. The distributor structure can be realized, for example, as a channel or else as an electrically conductive porous layer.

The function of the gas distributor structure on the anode side and cathode side is as follows:

the reactant gas or reactant water should be distributed evenly over the active surface,

the electrons should be conducted to the next battery,

liquid water or water vapor as reaction product and product gas is fed from the cell and

the heat generated by the catalyst layer should be discharged to the coolant.

According to the current state of the art, stamped sheet metal is used as the gas distributor structure. Thereby creating a spacer-channel structure. In a fuel cell, reactant gases are distributed to the electrochemically active surface through a channel structure. There is however a restricted gas flow under the septum. According to several literature sources, liquid product water can accumulate on the air side below the spacers, which product water impedes the gas transport to the catalyst layer. Thereby locally greatly hindering O toward the catalyst layer₂The power of the fuel cell is locally reduced by the transport, which leads to a deterioration of the overall performance of the entire fuel cell.

Channel structures are an alternative to open cell foams. These foams have a porosity of > 90%. The spacers inside the foam have a thickness of a few micrometers. No noticeable liquid water collects under the septum. This foam thus enables an optimized transport of the reaction products, liquid water. As a result, a higher flow density (i.e. a greater amount of product water) and thus an improved power density can be achieved by the foam structure compared to the channel structure. However, foams are relatively expensive to produce and the porous structure is arbitrary, since no oriented structure can be specified. For these reasons, foams have a high pressure loss compared to channels. This in turn leads to elevated requirements for an air compressor that presses air into the battery.

Instead of foam, wires or strands made of plastic, metal, carbon fiber or similar materials can also be used, which are connected to the fabric manually or mechanically by means of a weaving facility. The machines used for this purpose are mostly from the textile industry, but can be adapted to the aforementioned nonwoven materials by simple modification. The fabric is used in different fields. A fabric made of metal is used, for example, as a filter. A generally planar, approximately two-dimensional structure may be expanded into a three-dimensional mesh for some materials. This results in addition to the orthogonal filter directions in a filter plane in the fabric itself. The pore size and porosity of the fabric structure can vary over a wide range.

Disclosure of Invention

According to the invention, a gas distributor structure for a fuel cell or electrolyser, in particular a PEM fuel cell, is proposed, which has a fabric for distributing reactants, wherein the fabric has at least two fibers that differ from one another. The at least two mutually different fibers of the fabric are embodied as threads or strips which are made of a carrier material and extend in the vertical or horizontal direction, the carrier material being provided on the surface with a coating or a multi-layer coating of a functional material. As a result of the possibility of coating materials, more cost-effective materials, such as plastics or steel, are used instead of stainless steel and their properties are advantageously influenced by a suitable choice of the respective coating material, such as electrical conductivity of the fabric transversely to the direction of fluid flow, corrosion resistance, mechanical stability, water drainage and production costs. Thus, for example, the use of expensive corrosion-resistant stainless steel can be avoided, for example, when the carrier material, such as steel or plastic, is provided with a corresponding coating.

In other embodiments of the solution proposed according to the invention, the coating can be implemented as a single-layer coating or as a multi-layer coating and is made of, for example, an electrically conductive material. As the conductive material made into a single-layer coating or a multi-layer coating, for example, a material such as titanium, plastic, or stainless steel can be used. Noble elements, gold, palladium and platinum, can likewise be used in addition to the preferred materials, titanium and stainless steel. Furthermore, electrically conductive polymers or carbon-based coatings such as graphite are possible, such as coatings consisting of diamond-like carbon. For the case where the coating or coatings may be implemented from titanium, carbon or stainless steel, the carrier material may be selected from relatively cost-offset materials such as plastics or steel.

According to the solution proposed according to the invention, the coating (single-layer coating or multi-layer coating) serves as a corrosion protection for the carrier material, which may also be a material with a high mechanical strength, for example. The carrier material with higher mechanical strength may be, for example, martensitic steel. In addition to martensitic steels, it is also possible to use further, less corrosion-resistant, in particular optionally highly alloyed stainless steels.

On the other hand, the coating (configured as a single-layer coating or as a multi-layer coating) can also consist of a non-conductive material, such as PTFE.

In the gas distributor structure proposed according to the invention, the latter can advantageously be constructed in such a way that the contact points of the fabric with the bipolar plates of the fuel cell stack are free of electrically non-conductive material and/or are coated with electrically conductive material on the contact points. For this purpose, the contact points can be provided with a multilayer coating, wherein the layer made of electrically non-conductive material is selectively removed only at the contact points, so that an electrical conductivity is present at the contact points.

In an embodiment variant, the gas distributor structure proposed according to the invention can be provided, for example, with a coating, which is realized as a single-layer coating or as a multi-layer coating, only on a single side, i.e. either only on the front side or only on the rear side.

The gas distributor structure can also be realized in such a way that, for example, a first part of the fabric is provided with an electrically non-conductive or electrically conductive material, while a second part of the fabric, for example the part located below this first part, can be coated with a material different from this material.

In a further embodiment of the solution proposed according to the invention, it is possible, for example, to provide an active surface in the output region of the fuel cell, for example in the region in front of the second port arranged on the output side, as seen above the input side and the output side of the fuel cell, which active surface is provided with a textile fabric proposed according to the invention, preferably corrosion-resistant or specifically hydrophilic/hydrophobic coated, since the production of product water is most easily expected in this region.

Finally, a gas distributor structure is proposed according to the invention for use in a PEM fuel cell or electrolyser.

The use of expensive corrosion-resistant stainless steel can be avoided or significantly reduced by the gas distributor structure proposed according to the invention, since the respective properties in terms of corrosion resistance or improved electrical conductivity are applied to the wire or strip by the material selected for the respective coating. For example, electrical conductivity, corrosion resistance or mechanical stability transverse to the flow direction can also be improved in a targeted manner when martensitic steels and similar materials are used. On the other hand, the pressure loss of the fluid can be influenced by a suitable coating choice or a larger grid for a coarser mesh fabric or a finer fabric, and likewise the water drainage can be improved. Furthermore, a reduction in the production costs can be achieved by the gas distributor structure proposed according to the invention, since the use of expensive corrosion-resistant stainless steel can then be dispensed with and the corrosion resistance can be produced solely by the coating.

The coating consisting of electrically non-conductive and electrically conductive material also acts as a protection against corrosion of the gas-coated carrier material, which is plastic, steel or a material with improved electrical properties, such as copper or the like.

With regard to the manufacturing aspect of the gas distributor structure proposed according to the invention, the coating can be carried out both before and after the manufacture of the fabric. If the coating is applied after the production of the fabric, for example, a stepwise layer change can also be achieved, such as a coating that is implemented on only one side, either only on the front side or only on the rear side, of the fabric that acts as the gas distributor structure. Furthermore, the parts of the fabric are provided with different coatings according to functionality, for example, in order to control and influence the water discharge.

If the conductive coating is realized after the manufacture of the fabric, the following additional advantages result: at the crossing points in the fabric, i.e. where the horizontally and vertically arranged wires cross, the wire-to-wire transition resistance can be avoided in an advantageous manner, since here an electrical connection in terms of material can be established by means of the coating. The material connection produced can be improved, for example, by a subsequent heat treatment. Thus, an inexpensive wire fabric made of steel can be provided, for example, with a thin coating, for example with a hard solder. In the heat treatment, the solder melts and forms a material connection which can be provided with a corrosion-resistant coating in the second step.

If the coating process is carried out in the case of a single-thread coating, i.e. before the production of the fabric, the transition resistance can be minimized by a suitable choice of the coating material, for example in the case of a carbon coating.

Drawings

The invention is described in more detail below with reference to the accompanying drawings:

the figures show:

figure 1 is a schematic view of a fuel cell,

figure 2 is a stamped plate having a channel structure,

FIG. 3 is a three-dimensional representation of a press fabric made of fibers with different functional coatings,

figure 4 is a diagram of a layer construction according to the invention of a fuel cell,

figure 5 is a three-dimensional representation of the layer construction according to figure 4,

FIG. 6 is a front view of a multilayer coated fabric as an air distributor structure, an

Fig. 7 is a plan view of the cathode side (air side) of a fuel cell having inlet side and outlet side ports.

Detailed Description

A schematic representation of the fuel cell 10 can be seen from the representation according to fig. 1.

Fig. 1 shows a PEM fuel cell 10 in a schematic representation. The fuel cell stack 12 shown in fig. 1 comprises

gas distributor structures

14 and 23 and a water distribution structure 19, which in the embodiment according to fig. 1 is realized as a cooling channel 19. The uppermost structure 19 (cooling channel) is flowed through by a cooling medium 18, for example a cooling fluid, and the gas distributor structure 23 located below this structure is flowed through by a gas flow which is wetted with the optionally moistened H₂Composition, see position 20. The lowermost structure 14 is flowed through by the optionally humidified air 22. In the film layerOn both sides of 26 there are catalyst layers 16, 24 with a porous structure and a gas diffusion monolayer 27 consisting of carbon fibers.

Fig. 2 shows a stamped metal sheet with a channel structure.

The stamped metal sheet 40, which forms the channel structure 50, is known from the illustration according to fig. 2. The individual channels 70, which are configured in a basin shape 72, are separated from one another by a wall 60 running in the longitudinal direction. The channel 70 is configured in a basin shape 72 and includes a basin bottom 73 and a suitably oriented wall 60. Liquid water is designated by reference numeral 75 and collects below the channel structure 50, see position 75. The reactant gases are distributed via the channel structure 50 to the electrochemically active side of the fuel cell 10 according to the illustration in fig. 1. Reference numeral 27 indicates a gas diffusion monolayer, which is located above the membrane layer 26.

Fig. 3 shows the fabric 80 in a three-dimensional view.

Fig. 3 shows a three-dimensional view of the web 80 after punching out the channel structure 50, the web having a fluid flow direction 96 and a flow transport direction 98 as drawn. The fabric 80 according to the three-dimensional representation in fig. 3 has a wavy appearance, whereby a large surface is achieved, which in addition favorably influences the gas distribution and the pressure loss. The fabric 80 is formed by vertically extending wires 90 and horizontally extending wires 92 oriented perpendicular to the wires. At the ends of the wires there are contact points, for example for the fabric 80 used as a gas distributor structure to contact the bipolar plates of the PEM fuel cell 10.

Fig. 4 shows a diagram of the layer structure according to the invention of a fuel cell, in particular a PEM fuel cell.

As can be seen from fig. 4, between the film layers 26 with GD L27, there is a first stamped metal sheet 40 and a second flat sheet 42, respectively, between each next film layer 26 and second flat sheet 42 there is a fabric 80 embodied in the form of a wave-shaped stamping, which fabric comprises a wire 90 extending in the vertical direction by stamping and a wire 92 extending orthogonally thereto, i.e. horizontally.

The flow direction 98 extends in the vertical direction, whereas the fluid flow direction is designated by reference numeral 96 andextending in the plane of the drawing according to fig. 5. In each cavity formed by the first punched metal plate 40, H in a gaseous state₂And liquid water, for example, alternately.

As is also apparent from the illustration according to fig. 4, the fabric 80 has a substantially wave-shaped appearance. On the respective peaks of the web 80 and on the respective valleys of the web 80, the first contact points 44 are shown on one side with respect to the second plate 42, and the second contact points 46 are shown on the valleys of the web 80 in a wave-shaped configuration with respect to the adjoining film layer 26. Inside the

respective contact site

44 or 46 of the fabric 80, the fabric may be provided with a coating 100, see the illustration according to fig. 6. The transition resistance at the first and second contact points 44 and 46 can be optimized by means of the respective coating 100, which can be, for example, a coating consisting of an electrically conductive material 108, a corrosion-resistant material or also a non-conductive material 112.

Fig. 5 shows a three-dimensional representation of the fabric, which is shown from the front in a two-dimensional representation, i.e., in a front view, according to fig. 4.

As can be seen from fig. 5, the fabric 80 arranged in a wave-like manner is flowed through by the fluid in the X direction, which corresponds to the flow direction 96. The flow conveyance in the Z direction corresponding to the flow conveyance direction 98 takes place perpendicularly to the X direction, which is perpendicular to the fluid flow direction 96 according to the illustration in fig. 5. For the sake of simplicity, the threads 90 running in the vertical direction or the threads 92 running in the horizontal direction are not shown in the fabric 80 implemented in a wave shape.

Figure 6 shows a front view of a multilayer coated fabric.

The view shown in fig. 6 from the front shows a wave-shaped deformed fabric 80, which is formed from a material 104 to be coated, the material 104 to be coated can be a wire 90 running in the vertical direction or a wire 92 running in the horizontal direction, the structure shown in fig. 6 from the front comprises a second plate 42 and on the opposite side a membrane layer 26, which is also referred to as GD L (gas diffusion layer).

However, metals having intrinsically improved electrical conductivity, such as copper, can also be used as material 104 to be coated. With the corrosion protection shown by the coating 100, it is also possible to use other materials with a higher mechanical strength as the carrier 106, which may improve the mechanical stability, for example, when using martensitic steel as the carrier 106. The high mechanical strength of the wires 90, 92 or the flat strip 94 enables the production of a coarse mesh or the implementation of a finer mesh of the web 80, respectively, depending on the electrical conductivity.

The coating 100 or the multilayer coating 113 is, in contrast, made of a non-conductive material 112, which is particularly corrosion-resistant for this purpose, for example PTFE. Thereby improving water drainage from the PEM fuel cell 10 depending on the hydrophilic or hydrophobic properties of the coating 100 or the multi-layer coating 113.

In the case of a coating having a non-conductive material 112, the contact points of the fabric 80 may become conductive by: the non-conductive material 112 is removed at the respective contact points. This can be achieved, for example, by simple selective removal of the coating 100 at the contact points, for example by removal by the application of heat in the case of polymers, or by the coating 100 consisting of an electrically conductive material 108 there. It is also conceivable to apply a multilayer coating 113 in the region of the contact points, so that the electrically conductive material 108 is freely accessible after removal of the coating consisting of the electrically non-conductive material 112.

Coating 100, which is a single or multi-layer coating 113, can be achieved either before or after the manufacture of fabric 80. If the coating is effected after the manufacture of the fabric 80, it is also possible to effect a gradual layer change of the coating, for example only a one-sided coating of the fabric 80 on its front side or on its rear side. Furthermore, it is possible to apply the fabric 80 with a coating of an electrically conductive material 108, a corrosion-resistant material 110 and an electrically non-conductive material 112 in a first section (located above) and to provide the fabric 80 with a coating 100 different from the above-described coatings in a second section (located below), for example in order to control the drainage of water in the lower region.

On the first contact site 44 and on the second contact site 46, the fabric 80 is provided with a coating 100. The coating 100 is applied to a surface 102 of the material 104 to be coated, to be precise on the side facing the second plate 42 at the first contact point 44 and the membrane layer 26 opposite the second plate at the second contact point 46. Fig. 7 shows that in the region of the first contact points 44, an electrically conductive material 108 is provided on the surface 102, while in the region of the wave troughs of the fabric 80, a coating 100 consisting of a corrosion-resistant material 110 is provided in the region of the second contact points 46. The electrically conductive material 108 in the region of the first contact site 44 reduces the transition resistance of the metallic material of the second plate 42; the conductive material 108 is preferably a metallic material. The coating 100 applied to the surface 102 of the material 104 to be coated in the region of the wave troughs of the fabric 80 is, for example, a corrosion-resistant material 110 and has the task of exhibiting a small transition resistance. The corrosion resistant material 110 is, for example, carbon paper. In the configuration shown in fig. 6, the flow direction 98 runs counter to the direction of the Z axis, while the fluid flow direction 96, which in the illustration according to fig. 7 runs along the drawing plane, coincides with the X axis.

It can be seen from the illustration according to fig. 6 that the fabric 80 shown there has a multilayer coating 113 between the second plate 42 on the one hand and the membrane layer 26 on the other hand, which can be realized from different materials, in this example a conductive material 108 and a corrosion-resistant material 110, on the first contact point 44 or the second contact point 46. The different functionalities exhibited by the multilayer coating 113 on the fabric 80, which itself can be realized with relatively cost-effective materials with respect to the material 104 to be coated. The refining (Veredlung) of this material under the framework of the multilayer coating 113 yields a multilayer coating which is applied only at the contact points 44, 46, i.e. at those points of the material to be coated 104 which are to fulfill the respective function.

Fig. 7 shows a top view of a fuel cell with ports shown on the input side and the output side.

As can be seen from fig. 7, the PEM fuel cell 10 (shown here in a plan view) has a first port 118 on the inlet side 114, through which fluid enters the fuel cell 10 in the fluid flow direction 96. The PEM fuel cell 10 has a plurality of second ports 120 in the region of the outlet side 116, in which a fluid (H is present)₂And liquid water) is discharged from the PEM fuel cell 10 through the second port. FIG. 7 shows the combustion in PEMIn the case of the fuel cell 10, a coating 100 is applied which runs in the region of the outlet side 116, since here product water is most likely to occur and therefore, for example, the coating 100 is provided as an active surface 122, for example, by a corrosion-resistant material 110, in order to avoid damage in the region of the outlet side 116 of the PEM fuel cell 10 as a result of the product water produced.

The present invention is not limited to the embodiments and aspects shown and described herein. Rather, a number of variations within the processing scope of the person skilled in the art can be implemented within the scope of the invention described.

Claims

1. Gas distributor structure (14) for a fuel cell or electrolyser, in particular a PEM fuel cell (10), having a fabric (80) for distributing reactants, wherein the fabric (80) has at least two mutually different fibers (81, 82, 83), characterized in that the at least two mutually different fibers (81, 82, 83) of the fabric (80) are embodied as wires (90, 92) of a material (104) to be coated, which extends in a vertical direction or in a horizontal direction, which material to be coated is provided with a coating (100) or a multi-layer coating (113) of a functional material (108, 110, 112).

2. The gas distributor structure (14) according to claim 1, wherein the coating (100) or the multi-layer coating (113) is made of an electrically conductive material (108).

3. The gas distributor structure (14) according to claim 2, wherein the coating (100) or the multi-layer coating (113) comprises: titanium, carbon, stainless steel, or precious elements such as gold, palladium, platinum, conductive polymers or composites, e.g. polymers with carbon particles, or carbon based coatings such as graphite.

4. A gas distributor structure (14) according to claim 2 or 3, characterized in that plastic or steel is selected as the material (104) to be coated.

5. The gas distributor structure (14) according to claim 1, wherein the coating (100) or the multilayer coating (113) serves as a corrosion protection and uses a material (104) to be coated with a high mechanical strength.

6. The gas distributor structure (14) according to claim 5, wherein the material to be coated (104) having a higher mechanical strength is a martensitic steel.

7. The gas distributor structure (14) according to claim 1, wherein the coating (100) or the multi-layer coating (113) comprises an electrically non-conductive material (112), such as PTFE.

8. The gas distributor structure (14) according to claim 7, wherein the contact points of the fabric (80) with bipolar plates of a fuel cell stack (12) are free of the electrically non-conductive material (112) and/or coated with an electrically conductive material (108) at the contact points.

9. The gas distributor structure (14) according to claim 1, wherein the fabric (80) is provided with a coating (100) or a multi-layer coating (113) on one side on the front side or on the rear side.

10. A gas distributor structure (14) according to claim 1, wherein a first portion of the fabric (80) is provided with a non-conductive material (112) or a conductive material (108) and a second portion of the fabric (80) is coated with a material different from this material.

11. The gas distributor structure (14) according to claim 1, wherein the multilayer coating (113) is implemented as a site-dependent multilayer coating.

12. The gas distributor structure (14) according to claim 11, wherein the multilayer coating (113) comprises an electrically conductive material (118) in the region of the first contact locations (44) and a corrosion resistant material (110) in the region of the second contact locations (46).

13. Use of a gas distributor structure (14) according to any of claims 1 to 12 in a PEM fuel cell (10) or an electrolyser.