METHOD FOR PRODUCING A BIPOLAR PLATE FOR A FUEL CELL

Abstract

The invention relates to a method for producing a bipolar plate (10) for a fuel cell (1), comprising a plate body (11) for separating the fuel cell (1) from a neighbouring fuel cell (1) or a housing, wherein the plate body (11) has a flow field structure (1b) for introducing the reactants into the fuel cell (1). To that end, according to the invention, the method comprises the following steps: providing a mass (D1) made of electrically conductive particles and a polymer-based adhesive; applying the provided mass (D1) to the plate body (11) of the bipolar plate (10) in the form of the flow field structure (1b); pyrolising the applied mass (D1) which remains on the plate body (11) of the bipolar plate (10) as a shaping element in the form of the flow field structure (1b) and which is connected to said plate body.

Claims

1. A method for producing a bipolar plate (10) for a fuel cell (1), comprising: a plate body (11) for separating the fuel cell (1) from a neighboring fuel cell (1) or a housing, the plate body (11) having a flow field structure (1b) for introducing reactants into the fuel cell (1), wherein the method comprises: providing a mass (D1) of electronically conductive particles and a polymer-based adhesive, applying the provided mass (D1) in the form of the flow field structure (1b) to the plate body (11) of the bipolar plate (10), pyrolyzing the applied mass (D1) which remains as a shaping element in the form of the flow field structure (1b) on the plate body (11) of the bipolar plate (10) and is connected to said body.

2. The method as claimed in claim 1, wherein a negative structure (1a), which can be burned out is applied to the plate body (11) of the bipolar plate (10) before the flow field structure (1b) is applied to the plate body (11) of the bipolar plate (10).

3. The method as claimed in claim 2, wherein the negative structure (1a) which can be burned out is provided as a mixture of particles and binder having a similar softening temperature and/or decomposition temperature lying below a decomposition temperature of the electronically conductive particles of the mass (D1).

4. The method as claimed in claim 3, wherein the particles of the negative structure (1a) which can be burned out comprise at least one of the following elements: polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC) and/or polyetheretherketone (PEEK), and/or wherein the binder of the negative structure (1a) which can be burned out comprises at least one of the following elements: polyethylene glycol (PEO), and/or polyvinylidene fluoride (PVDF) and/or acrylate adhesive.

5. The method as claimed in claim 1, wherein the electronically conductive particles of the mass (D1) comprise graphite particles and/or graphite fibers, and/or wherein at least some of the electronically conductive particles of the mass (D1) have a magnitude of 10 μm to 50 μm.

6. The method as claimed in claim 1, wherein the polymer-based adhesive of the mass (D1) comprises at least one of the following elements: acrylate adhesive and/or polytetrafluoroethylene (PTFE) and/or polyvinylidene fluoride (PVDF).

7. The method as claimed in claim 1, wherein the mass (D1) comprises particles which can be burned out for forming macroscopic pores within the flow field structure (1b).

8. The method as claimed in claim 1, wherein the provided mass (D1) is applied in the form of flow field structure (1b) to the plate body (11) of the bipolar plate (10) by a printing technique.

9. The method as claimed in claim 1, wherein after the pyrolyzing of the applied mass (D1) in the form of the flow field structure (1b) on the plate body (11) of the bipolar plate (10), a gas diffusion layer (GDL) and/or a microporous layer (MPL) are/is applied to the flow field structure (1b), composed of a second mass (D2) which is different than the first mass (D1), or wherein a gas diffusion layer (GDL) and/or a microporous layer (MPL) are/is applied together with the flow field structure (1b) of the first mass (D1) to the plate body (11) of the bipolar plate (10).

10. A bipolar plate (10) for a fuel cell (1), comprising: a plate body (11) for separating the fuel cell (1) from a neighboring fuel cell (1) or a housing, the plate body (11) comprising flow field structure (1b) for introducing reactants into the fuel cell (1), wherein the flow field structure (1b) is applied by means of a mass (D1) of electronically conductive particles and a polymer-based adhesive to the plate body (11) of the bipolar plate (10) and is pyrolyzed.

11. (canceled)

12. A fuel cell (1) comprising at least one bipolar plate (10) as claimed in claim 10.

13. The method as claimed in claim 7, wherein the particles which can be burned out include polymethyl methacrylate (PMMA).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention and developments thereof and also advantages thereof are elucidated in more detail below with reference to drawings. The drawings, in each case schematic, are as follows:

[0032] FIG. 1 shows an illustrative construction of a fuel cell in the sense of the invention,

[0033] FIG. 2 shows an illustrative construction of a fuel cell having a bipolar plate in the sense of the invention, and

[0034] FIG. 3 shows a plan view with multiple side views of a bipolar plate in the sense of the invention.

DETAILED DESCRIPTION

[0035] In the various figures, identical parts of the invention are always provided with the same reference symbols, which for that reason are generally described only once.

[0036] FIGS. 1 to 3 are intended to serve to describe a method of the invention for producing a bipolar plate 10 fora fuel cell 1.

[0037] An illustrative fuel cell 1 is shown in FIG. 1. It comprises a membrane M, provided on both sides with one electrode lamina EA each. In the cathode region K of the fuel cell 1, the electrode lamina EA is adjoined by a microporous layer MPL and a gas diffusion layer GDL. A distribution structure for the fuel cell 1 with corresponding cavity structures 11 in a millimeter range is formed by a bipolar plate 10 which comprises cavity structures 11 in the form of elevations. Known bipolar plates 10 may also be provided with cavity structures 11 by forming.

[0038] The method of the invention serves for producing a bipolar plate 10 for a fuel cell 1 that is shown in FIG. 2 and that comprises a (preferably planar) plate body 11 for separating the fuel cell 1 from another fuel cell 1 or a housing, the plate body 11 comprising a flow field structure 1b for introducing the reactants into the fuel cell 1.

[0039] For this, the method of the invention comprises the following steps:

[0040] providing a (first) mass D1, such as a printing paste or a dispersion, of electronically conductive particles and a polymer-based adhesive,

[0041] applying the provided mass D1 or dispersion in the form of the flow field structure 1b to the plate body 11 of the bipolar plate 10, by a printing technique, more particularly a screen printing technique, for example,

[0042] pyrolyzing the applied mass D1 or dispersion which remains as a shaping element in the form of the flow field structure 1b on the plate body 11 of the bipolar plate 10 and is connected to said body.

[0043] The fuel cell 1 of the invention may be stacked to form a fuel cell stack having a plurality of stacked repeating units, in the form of PEM fuel cells, for example.

[0044] The bipolar plate 10 of the invention provides a cavity structure or a channel structure in a millimeter range for the coarse distribution of reactants in the fuel cell 1. The bipolar plate 10 of the invention may be used advantageously with a planar or flat plate body 11, which is particularly advantageous to produce.

[0045] Subsequently or together with the flow field structure 1b, a porous gas diffusion layer GDL and optionally a microporous layer MPL may be applied, more particularly by co-printing, to the plate body 11 (cf. FIG. 3).

[0046] As is evident from FIGS. 2 and 3, the flow field structure 1b of the invention comprises not only the outer cavity structure or channel structure in a millimeter range but also an inner porosity. The flow field structure 1b of the invention may be used preferably in the cathode region K of the fuel cell 1, in order to promote the removal of the product water there.

[0047] According to the invention, the bipolar plate 10 with the flow field structure 1b of the invention and with optionally a subsequent gas diffusion layer GDL and/or optionally a subsequent microporous layer MPL is pyrolyzed together with the plate body 11. In this way it is possible to provide a bipolar plate 10 having improved electrical, more particularly electronic, and thermal connection properties between the plate body 11, the porous flow field structure 1b, and the gas diffusion layer GDL and/or the microporous layer MPL.

[0048] As indicated by FIGS. 2 and 3, the flow field structure 1b may have a corrugated structure, having a semicircular cross section at the webs, for example. In this way it is possible to enable a uniform, preferably reduced, tracking force on the membrane M. The flow field structure 1b may have a porosity of approximately 50% to 70%.

[0049] As indicated schematically by FIGS. 2 and 3, before the flow field structure 1b is applied, more particularly by printing, to the plate body 11 of the bipolar plate 10, a negative structure 1a which can be burned out may be applied to the plate body 11 of the bipolar plate 10, this structure being completely or near-completely decomposed subsequently, during the pyrolyzing, into gaseous components. The negative structure 1a which can be burned out may be provided as a mixture, such as a drying dispersion, of particles and binder, having a similar softening temperature and/or decomposition temperature, lying preferably below a decomposition temperature of the electronically conductive particles and/or of the polymer-based adhesive of the mass D1. The particles of the negative structure 1a which can be burned out may comprise at least one of the following elements: polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC) and/or polyetheretherketone (PEEK). The binder of the negative structure 1a which can be burned out may comprise at least one of the following elements: polyethylene glycol (PEO), polyvinylidene fluoride (PVDF) and/or acrylate adhesive.

[0050] The electronically conductive particles of the mass D1 may in turn comprise graphite particles and/or graphite fibers, and the electronically conductive particles of the mass D1 may have a magnitude of 10 μm to 50 μm. The polymer-based adhesive of the mass D1 may comprise at least one of the following elements: acrylate adhesive and/or polytetrafluoroethylene (PTFE) and/or polyvinylidene fluoride (PVDF).

[0051] Optionally it is conceivable that the mass D1 may comprise particles which can be burned out, polymethyl methacrylate (PMMA) for example, for forming macroscopic pores within the flow field structure 1b.

[0052] As shown by FIG. 3 in the side view 1), a gas diffusion layer GDL and/or a microporous layer MPL may be applied by printing or placing to the flow field structure 1b, composed of a second mass D2, which is different, more particularly finer, than the (first) mass D1, after the pyrolyzing of the flow field structure 1b on the plate body 11 of the bipolar plate 10. In this case it is conceivable that the electronically conductive particles of the finer mass D2 may have a smaller particle size than the (first) mass D1. It is therefore possible to enable a bipolar plate 10 having a plurality of layers and having different particle sizes and pore sizes, in order to promote improved introduction of reactants into the fuel cell 1 and subsequently a uniform distribution of the reactants over the membrane M of the fuel cell 1.

[0053] As shown by FIG. 3 in the side view 2), a gas diffusion layer GDL and/or a microporous layer MPL may be printed together with the flow field structure 1b of the (first) mass D1 on the plate body 11 of the bipolar plate 10. Accordingly it is possible to enable a particularly inexpensive and simple bipolar plate 10.

[0054] The above description of the figures describes the present invention exclusively in the context of examples. It will be appreciated that, insofar as it makes technical sense, individual features of the embodiments may be freely combined with one another without departing from the scope of the invention.