WO2019175200A1

WO2019175200A1 - Gas distributor structure for a fuel cell

Info

Publication number: WO2019175200A1
Application number: PCT/EP2019/056202
Authority: WO
Inventors: Martin Schoepf; Arne Stephen FISCHER
Original assignee: Robert Bosch Gmbh
Priority date: 2018-03-14
Filing date: 2019-03-13
Publication date: 2019-09-19
Also published as: DE102018203828A1

Abstract

The invention relates to a gas distributor structure (10) for a fuel cell (100), which is used to provide a reactant to the fuel cell (100), having: a first region (11) with a first distributor structure (S1) and with a second, subsequent distributor structure (S2) for distributing the reactant in the fuel cell (100), the first region (11) being adjacent to a flow field plate (101) of the fuel cell (100); and a second region (12) with a third sub-ordinate distributor structure (S3), for uniformly distributing the reactant over a membrane electrode assembly (103) of the fuel cell (100), the second region (12) being adjacent to the membrane electrode assembly (103), wherein the first region (11) is formed by a foam structure (S), and the second region (12) is formed by a gas diffusion layer (GDL).

Description

description

Gas distributor structure for a fuel cell

The invention relates to a gas distributor structure for a fuel cell, in particular a PEM fuel cell, or for an electrolyzer, which serves to provide a reactant to the fuel cell, according to the independent device claim. Furthermore, the invention relates to a

Fuel cell with at least one corresponding gas distributor structure according to the independent device claim.

State of the art

Fuel cells are electrochemical energy converters. In fuel cells, hydrogen H2 and oxygen 02 are converted into water H20, electrical energy and heat for energy. Fuel cells essentially comprise five components (see Figure 1 or la prior art). In the middle there is a proton-conductive membrane 103, for example a polymer membrane. The membrane 103 is embedded between two gas diffusion layers GDL of microporous graphite paper or graphite fabric, wherein either the membrane 103 or the gas diffusion layers GDL to the

Contact surfaces with a catalyst material, for example. Platinum, is coated for the electrochemical reaction. The gas diffusion layers GDL are in turn arranged between two bipolar plates 101, 102. A stack or repeating unit of this construction forms a (fuel cell) stack.

The bipolar plates 101, 102 take over the coarse distribution of the operating media (air or oxygen 02 on the cathode side K and hydrogen H2 on the anode side A and cooling water H20). Finally, the microporous gas diffusion layers GDL take over the fine distribution over the active surface and the supply of the reaction gases of the active surface of the membrane 103 and the removal of product water H20 from the membrane 103 into the coarse structure of the bipolar plates 101, 102.

To assure the coarse distribution of the operating media with a low pressure loss and at low cost, an exemplary bipolar plate 101 (and 102) of the prior art is made by embossing a channel structure into a sheet about 0.1 mm thick (see below in the figure la). However, the problem here is the accumulation of water in the gas diffusion layers GDL under the webs of the bipolar plate 101 on the cathode side K of the fuel cell 100 *.

Another exemplary coarse gas distributor structure of the prior art is shown in Figure 1b, which is made of an open-pore, electrically conductive foam S (e.g., metal, e.g., stainless steel, or graphite).

The use of foam structures S as gas distribution structures has u compared to embossed sheets. a. the advantage that the edition on the

Gas diffusion layer GDL in the case of a foam can be uniform or homogeneous, since the individual contact points are finer. In this way, the risk of product water accumulation in the gas diffusion layer GDL decreases, which can lead to the blockage of parts of the membrane 103. The problem with the foam structures S is the provision of the process gases in sufficient quantity or the provision of a sufficient process gas flow.

Disclosure of the invention

The invention provides a gas distributor structure for a fuel cell,

in particular a PEM fuel cell, or for an electrolyzer, which serves to provide a reactant to the fuel cell, with the features of the independent device claim and a fuel cell with at least one corresponding gas distributor structure with the features of the independent independent device claim. Other advantages, Features and details of the invention will become apparent from the dependent claims, the description and the drawings. In this case, features and details that are described in connection with the gas distributor structure according to the invention apply, of course, also in connection with the fuel cell according to the invention and in each case vice versa, so that with respect to the disclosure of the individual aspects of the invention always reciprocal reference is or may be.

The present invention provides a gas distributor structure for a fuel cell, in particular a PEM fuel cell, or an electrolyzer, which serves for providing a reactant to the fuel cell, comprising a first region with a first, in particular coarse, distributor structure and with a second downstream distributor structure Distributing the reactant in the fuel cell, wherein the first region of a bipolar plate of the fuel cell, which may now be formed in the form of a thin plate, adjacent, and a second region having a third, in particular fine or subordinate arranged distribution structure for uniform distribution the reactant over a membrane electrode assembly of the fuel cell, wherein the second region is adjacent to the membrane electrode assembly, and wherein the first region is formed by a foam structure and the second region by a gas diffusion layer.

The gas distributor structure according to the invention may preferably be located on the

Cathode side of the fuel cell may be provided to prevent accumulation of water on the membrane and to allow the distribution of the reactant with low pressure drops and low cost in the design and operation of a compressor. Furthermore, the gas distributor structure according to the invention may be provided on both sides, the cathode side and the anode side, of the fuel cell in order to favor the gas flow on both sides of the fuel cell. As a membrane electrode unit can be understood in the context of the invention, a membrane which can be coated with a catalyst material for the electrochemical reaction, for example. Platinum. As already mentioned above, when used as a gas distributor in a fuel cell, a foam structure (ie, an open-pore foam layer) has the advantage of a much finer and more uniform support on the gas diffusion layer than conventional embossed sheets. At the same time, a foam structure has the disadvantage that the flow resistance for the gas flow tends to be relatively high. To both, a homogeneous edition on the gas diffusion layer and a low flow resistance, too

The invention proposes to ensure that the side of the foam structure facing away from the gas diffusion layer, e.g. Using Multi Wire Electrical Discharge Machining (MWEDM) to provide a first, in particular coarse, distribution structure for the gas flow.

An idea of the invention lies in the fact that the first region for roughly distributing the reactant in the fuel cell is formed by a foam structure. The foam structure according to the invention again has two distributor structures of different sizes. The first

Distributor structure on the foam structure serves the coarse distribution of

Reactants in the fuel cell to reduce pressure losses when distributing the

To reduce reactants. This first or coarse distribution structure is ensured by the outer shape, for example. With relatively coarse grooves, the foam structure at the boundary to the flat bipolar plate. The second distribution structure, which is subordinate to the first distribution structure, is by the inner

Provided composition of the foam structure, so through the open pores of the foam. This second distribution structure now distributes the reactant more uniformly over the gas diffusion layer (or the second region) and simultaneously has many small and finely distributed contact points on the

Gas diffusion layer on to reduce the contact pressure and the contact surface at the individual points and to prevent water retention. The first area has for this purpose a flat bottom at the border to

Gas diffusion layer (ie the second area) on. Finally, the reactant is uniformly distributed over the active area of the membrane-electrode assembly through the second region formed by the gas diffusion layer, which has an even finer manifold structure. The first distribution structure at the foam structure at the border to the

Bipolar plate may have different shapes or characteristics.

For example. can the individual elements of the first distribution structure

different, z. B.

have (semi-) circular, rectangular or triangular cross-sectional shapes and combined cross-sectional shapes. The size, the distribution and the distances between the individual elements of the first distribution structure can also vary.

By means of the invention, the advantages of the foam structure are combined with the advantages of a pressure loss-reduced distribution of the reactant through a coarse distribution structure. At the same time, the presence of a classical channel structure, the risk of water retention at the

Cathode side of the membrane electrode unit reliably eliminated or at least substantially reduced.

Furthermore, it can be provided in the context of the invention in a gas distributor structure, that the foam structure is formed of a metal foam or a coated plastic foam. Thus, an open-pored structure with a high porosity can be made possible. In addition, a conduction of the electric current with a low electrical resistance and a good thermal conductivity can thus be ensured by the foam structure.

Furthermore, it is conceivable that the gas diffusion layer is formed from a paper-like or fabric-like carbon material or carbon paper. Thus, by the internal composition of the gas diffusion layer, a fine distribution of the reactants over the active area of the membrane-electrode unit can be made possible.

Likewise, with a gas distributor structure, the invention may provide that the first region in the distributor plane of the reactant (or the first

Distribution structure) has a periodic or a stochastic shape. Due to the periodic first distribution structure, the gas flow to a easy to set and forecast. Due to the stochastic first distribution structure, the gas flow can be well distributed.

In addition, in a gas distributor structure, the invention may provide that the first region has a sinusoidal shape, an angular shape, or a groove shape as viewed in cross-section with respect to a flow direction of the reactant. By means of a sinusoidal shape, a uniform transition of the reactant from the first distributor structure into the second distributor structure can be achieved and the surface area can be increased for this purpose. In addition, this can reduce the bearing surface between the gas distributor structure and the bipolar plate, whereby the accumulations of product water in the cell can be further reduced. By an angular shape or a groove shape, the production of the first distribution structure can be simplified. In the context of the invention, it is conceivable that the first region of the gas distributor structure can be formed with two distributor structures of different sizes in a single mold. Furthermore, it is conceivable for the first area of the gas distributor structure to be produced from a block, wherein corresponding structural elements can be produced on the upper side of the block by ablation or targeted deformation or compression of the material of the foam structure.

In addition, in the case of a gas distributor structure, the invention may provide for the first region in the distributor plane of the reactant to have a plurality of parallel, widthwise, or height-wise or alternately tapered, equally long or differently long grooves and / or elevations. By parallel grooves and / or elevations, the production of the first distribution structure can be simplified. By tapering grooves and / or surveys, the pressure drop when distributing the reactant can be selectively influenced, for example, be reduced and the conditions within the cell the various

Requirements at the respective places (eg beginning, middle, end of flow field). With alternating grooves, it may be advantageous to introduce the reactant from different directions into the

Initiate fuel cell. Since the transition from the first distributor structure into the second distributor structure takes place through the pores of the foam structure, the grooves and / or elevations need not extend over the entire length of the gas flow be formed. As a result, the stability of the gas distributor structure can be increased.

Furthermore, in the case of a gas distributor structure, the invention may provide that the second region forms a planar position parallel to the membrane electrode unit of the fuel cell. Thus, it can be ensured that the now finely divided reactant is uniformly added to the active area on the membrane electrode unit. In addition, thereby the electrical connection to the active surface of the membrane electrode unit can be reliably produced.

It is also possible that the first area is formed using Electrical Discharge Machining or Multi Wire Electrical Discharge Machining. Thus, a fine-pored foam structure can be provided whose pore size can be adjusted independently of the dimensions of the foam structure. In addition, this allows a rapid and cost-effective production of gas distributor structures in the context of the invention.

Furthermore, it can be provided that the first region and the second region are bonded to one another in a material-locking manner and / or by compression. Thus, an electrical connection with a low electrical

Resistance and a good thermal conductivity between the first and the second area can be achieved.

Furthermore, the invention provides a fuel cell which has at least one gas distributor structure on a cathode side and / or on an anode side, which can be designed as described above. With the help of

Fuel cell according to the invention, the same advantages can be achieved, the above in connection with the inventive

Gas distribution structure have been described. In the present case, full reference is made to these advantages.

Preferred embodiments: The gas distributor structure according to the invention and the inventive

Fuel cell and its developments and advantages thereof are explained below with reference to drawings. Each show schematically:

1 a shows an exemplary fuel cell according to the prior art,

Fig. Lb is another exemplary fuel cell according to the prior

Technology,

2 shows an exemplary fuel cell according to the invention,

Fig. 3 shows an exemplary gas distributor structure according to the invention for a

Fuel cell according to FIG. 2,

4 different examples of a gas distributor structure in the sense of

Invention in cross section through the gas distributor structure, and

5 different examples of a gas distributor structure in the sense of

Invention in a plan view of the gas distributor structure.

In the different figures, identical parts of the invention are always provided with the same reference numerals, which is why they are usually described only once.

FIG. 1 a shows a first example of a known fuel cell 100 *, which may be designed as described above. In the fuel cell 100 * according to the figure la, a gas distributor structure 10 * is used, the one

Gas diffusion layer GDL for a fine distribution and a bipolar plate 101 in the form of an embossed sheet for a coarse distribution of the reactant comprises. However, there is the risk of water accumulation under the webs of the embossed sheet of the bipolar plate 101. The areas of the active surface of the membrane 103 can thereby be blocked. Thus, the diffusion of the hydrogen ions H ⁺ through the diaphragm 103 can be hindered and the operation of the fuel cell 100 * can be disturbed. In addition, through the Webs of the embossed sheet, the underlying areas of the gas diffusion layer GDL are deformed. In addition, the gas flow of the reactants under the webs of the bipolar plates 101, 102 can be hindered by the water accumulation.

FIG. 1b shows a further example of a known fuel cell 100 **, which may be designed as described above. In this fuel cell 100 ** is at least on the cathode side K of the membrane 103, a gas distributor structure 10 ** used from an electrically conductive foam, which is delimited by a flat bipolar plate 101 from the anode region A. However, the gas supply is made possible only with considerable pressure losses. In such a fuel cell 100 ** high demands are placed on the compressor for providing the cathode air, the high cost and

Energy losses go along.

The invention will be explained below with reference to FIGS. 2 to 5.

As shown in FIG. 2, the present invention provides a gas distributor structure 10 for a fuel cell 100, for example a PEM fuel cell, or for an electrolyzer, which serves to supply a reactant to the fuel cell 100. In this case, the gas distributor structure 10 according to the invention comprises a first region 11 with a first, in particular coarse, distributor structure S1 and with a second downstream distributor structure S2 for distributing the reactant in the fuel cell 100, wherein the first region 11 adjoins a bipolar plate 101 of the fuel cell 100 the bipolar plate 101 may now be formed in the form of a thin and flat plate. In addition, the gas distributor structure 10 according to the invention comprises a second region 12 with a third, in particular fine or the first distribution structure S1 and the second distribution structure S2 subordinate distribution structure S3 for uniformly distributing the reactant over a membrane electrode unit 103 of the fuel cell 100, wherein the second region 12 adjoins the membrane electrode unit 103. According to the invention, it is provided that the first region 11 is formed by a foam structure S and the second region 12 by a gas diffusion layer GDL. Between the first region 11 and the second region 12, a transition in the form of a planar layer (part of region 11) is provided. In addition, the second region 12 forms a likewise planar position at the transition to the membrane electrode unit 103. At the transition to the flat bipolar plate 101, the shape of the upper side of the foam structure S is the first or coarse

Distributor structure S1 formed in the order of 0.1 mm to 1.5 mm. Meant here are the dimensions of the individual structural elements of the first distribution structure Sl. The height of the grooves of S1 may be 0.05 mm to 0.5 mm. It is particularly advantageous that all of these variables are decoupled from the pore size of the foam structure S.

The gas distributor structure 10 according to the invention may preferably be advantageous on the cathode side K of the fuel cell 100 in order to avoid accumulations of water on the membrane electrode unit 103 and to allow the distribution of the reactant with low pressure losses.

However, it is also conceivable, although not shown in the figures, that the inventive gas distributor structure 10 also on the

Anodenseite A of the fuel cell 100 may be advantageous to favor the gas flow of the reactants on both sides A, K of the fuel cell 100. The membrane electrode unit 103 in the context of the invention can be formed by a membrane 103 with a catalyst layer for triggering and promoting the electrochemical reaction, for example of platinum.

The foam structure S in the context of the invention forms the first region 11 of the gas distributor structure 10 according to the invention at the transition to the gas diffusion layer GDL, ie the second region 12 in the context of the invention, the foam structure S forms in particular compared to conventional embossed sheets the advantage of a lot finer and more even edition. At the same time forms the foam structure of the invention S at the transition to the bipolar plate 101 a coarse distribution structure Sl, so that the flow resistance for the gas flow is reduced in an advantageous manner. In isolation, the foam structure S according to the invention is shown in FIG.

In other words, the gas distributor structure 10 according to the invention offers both a homogeneous support on the gas diffusion layer GDL and a small one Flow resistance during insertion of the reactant into the fuel cell 100. The first distribution structure S1 on the side facing away from the gas diffusion layer GDL side of the foam structure S can advantageously by means of an Electrical Discharge Machining (EDM) or a Multi Wire Electrical Discharge

Machining (MWEDM).

The foam structure S thus has two distributor structures of different sizes (S1 and S2). The first distributor structure S1 serves for the coarse distribution of the reactant in the fuel cell 100. The second

Distributor structure S2, which is subordinate to the first distributor structure S1, is provided by the internal composition of the foam structure S, ie by the open pores of the foam structure S. Finally, the second region 12 with the finest third distributor structure S3 serves a uniform distribution of the reactant over the active Surface of the membrane electrode unit 103.

The gas diffusion layer GDL can be characterized by a finely porous, fibrous or

fabric-like structure made of carbon or graphite.

The first distribution structure S1 for resting on the bipolar plate 101 may have different shapes or expressions, as it is in

Below the figures 4 and 5 show.

As FIG. 4 shows, the individual elements of the first

Distribution structure S1 in the form of different polygonal, rounded or triangular structural elements, for example, grooves are formed, which can vary in size and which may be formed at different distances from each other. However, the forms mentioned are to be considered as exemplary embodiments only and may be different.

As FIG. 5 also shows, the first region 11 in the

Distributor level x, y of the reactant have multiple parallel, tapered or alternately tapered, equal length or different lengths grooves R and / or elevations E as structural elements. It is obvious that the grooves R and / or elevations E do not need to be formed over the entire length of the gas flow, since the transition from the first distributor structure S1 into the second distributor structure S2 takes place through the pores of the foam structure S.

Thus, with the aid of the invention, a gas distributor structure 10 can be provided which forms a uniform support on the gas diffusion layer GDL and which allows a low flow resistance in the distribution of the reactant in the fuel cell 100. Thus, the danger of

Water accumulation on the cathode side K of the membrane electrode unit

103 are reliably reduced and a compact compressor are made possible, which requires little power for its operation.

The above description of FIGS. 2 to 5 describes the present invention purely by way of example. Of course, individual features of the embodiments, insofar as it is technically feasible, can be freely combined with one another without departing from the scope of the invention.

Claims

claims

A gas distributor structure (10) for a fuel cell (100), which is used for

Providing a reactant to the fuel cell (100), comprising:

a first region (11) having a first distributor structure (S1) and having a second downstream distributor structure (S2) for distributing the reactant in the fuel cell (100),

wherein the first region (11) adjoins a bipolar plate (101) of the fuel cell (100),

and a second area (12) with a third subordinate,

Distribution structure (S3) for uniformly distributing the reactant over a membrane electrode assembly (103) of the fuel cell (100), the second region (12) being adjacent to the membrane electrode assembly (103),

and wherein the first region (11) is formed by a foam structure (S) and the second region (12) by a gas diffusion layer (GDL).

2. Gas distributor structure (10) according to claim 1,

characterized,

the foam structure (S) is formed from a metal foam or from a coated plastic foam,

and / or that the gas diffusion layer (GDL) is formed of a fibrous or web-like carbon material.

3. Gas distributor structure (10) according to one of the preceding claims, characterized in that

in that the first region (11) in the distributor plane (x, y) of the reactant has a periodic or a stochastic form.

4. Gas distributor structure (10) according to one of the preceding claims, characterized in that

the first region (11) has a sinusoidal shape, a polygonal shape or a groove shape when viewed in cross-section with respect to a flow direction (x) of the reactant.

5. Gas distributor structure (10) according to one of the preceding claims, characterized in that

in that the first region (11) in the distributor plane (x, y) of the reactant has a plurality of parallel grooves (R) and / or elevations (E) tapering or tapering in width and / or height ,

6. Gas distributor structure (10) according to one of the preceding claims, characterized in that

in that the second region (12) forms a planar position parallel to the membrane electrode unit (103) of the fuel cell (100).

7. Gas distributor structure (10) according to one of the preceding claims, characterized in that

that the first region (11) is formed by means of electrical discharge machining (EDM) or multi-wire electrical discharge machining (MWEDM).

8. Gas distributor structure (10) according to one of the preceding claims, characterized in that

the first region (11) and the second region (12) are connected to one another in a material-locking manner and / or by compression.

9. Fuel cell (100) having at least one gas distributor structure (10) according to one of the preceding claims on a cathode side (K) and / or on an anode side (A).