METHOD FOR PRODUCING A POROUS TRANSPORT LAYER FOR AN ELECTROCHEMICAL CELL

Abstract

A method for manufacturing a porous transport layer (4) of an electrochemical cell includes mixing a metal powder with a binder and a subsequent shaping-out into a foil. The foil is brought to bear on a porous metal layer (8). The binder is subsequently removed and the remaining brown part layer (9) is sintered to the porous metal layer (8), so that a porous transport layer (4) is formed which includes a porous metal layer (8) with a microporous metal layer (9) which is deposited thereon.

Claims

1. A method for manufacturing a porous transport layer for an electrochemical cell, the method comprising: mixing a metal, which is to form part of the transport layer, as a metal powder with a binder and subsequently shaping out the mixture into an extensive element or depositing the mixture onto a carrier foil as an extensive element; bringing the extensive element to bear on a porous metal layer (8) or on a green part or brown part of a porous metal layer; removing the binder and/or the carrier foil to provide a remaining brown part layer; and sintering the remaining brown part layer diffusion welding the remaining brown part layer to connect the remaining brown part layer to the porous metal layer or to the brown part of the porous metal layer.

2. A method according to claim 1, wherein the shaping-out of the extensive element into a foil is effected.

3. A method according to claim 2, wherein the shaping-out of the foil is effected by extruding.

4. A method according to claim 2, wherein the shaping-out of the foil is effected by way of continuous casting.

5. A method according to claim 2, wherein the shaping-out of the foil is effected by calendering.

6. A method according to claim 1, wherein the extensive element is deposited onto the porous metal layer or onto the brown part of the porous metallic layer in a screen printing method.

7. A method according to claim 1, wherein the porous metallic layer is formed by metal powder which is mixed with binder, wherein the green part is formed after the shaping-out and the binder is subsequently removed and the formed brown part is sintered.

8. A method according to claim 7, wherein the removing of the binder and/or the sintering is effected simultaneously with that of the extensive element.

9. A method according to claim 1, wherein the metal is titanium or an alloy which is based at least to 95% by weight on titanium

10. A method according to claim 1, wherein the porous metal layer is formed by a sinter metal plate, a metal fabric and/or metal felt.

11. A method according to claim 1, wherein the metal powder with a maximal grain size smaller than 45 μm, is used for manufacturing the extensive element.

12. A method according to claim 1, wherein a surface of the porous transport layer at a side for bearing on a catalyzer is smoothed by way of grinding or rolling.

13. A method according to claim 1, wherein a surface of the porous transport layer on a side for bearing on a catalyzer is roughened chemically.

14. A method according to claim 1, wherein the extensive element foil is formed in a thickness of 0.04 mm to 0.2 mm.

15. A method according to claim 1, wherein the transport layer is welded to a bipolar plate.

16. A porous transport layer, manufactured according to a method comprising: mixing a metal, which is to form part of the transport layer, as a metal powder with a binder and subsequently shaping out the mixture into an extensive element or depositing the mixture onto a carrier foil as an extensive element; bringing the extensive element to bear on a porous metal layer or on a green part or brown part of a porous metal layer; removing the binder and/or the carrier foil to provide a remaining brown part layer; and sintering the remaining brown part layer or diffusion welding the remaining brown part layer to connect the remaining brown part layer to the porous metal layer or to the brown part of the porous metal layer.

17. A porous transport layer according to claim 16, wherein the shaping-out of the mixture, into the extensive element forms a foil.

18. A porous transport layer according to claim 17, wherein the shaping-out of the foil is effected by extruding.

19. A porous transport layer according to claim 17, wherein the shaping-out of the foil is effected by way of continuous casting.

20. A porous transport layer according to claim 17, wherein the shaping-out of the foil is effected by calendering.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the drawings:

[0030] FIG. 1 is a greatly simplified schematic sectioned representation showing the construction of electrolysis cell of a PEM electrolyzer;

[0031] FIG. 2 is a schematic sectioned representation showing the extruding of a foil which is formed from metal foil and binder;

[0032] FIG. 3 is an enlarged sectioned representation showing the construction of the foil;

[0033] FIG. 4 is an enlarged sectioned representation showing foil which is applied onto the porous metal layer;

[0034] FIG. 4a is an enlarged sectioned representation showing the foil which is applied onto a green part of the porous metal layer;

[0035] FIG. 5 is an enlarged sectioned representation showing the arrangement according to FIG. 4 after removing the binder;

[0036] FIG. 6 is an enlarged representation in section showing the porous transport layer on an upper surface after the smoothing;

[0037] FIG. 7 is an enlarged representation in section showing the surface of the layer after the roughening;

[0038] FIG. 8 is a schematic representation showing the depositing of the mass which consists of the metal powder and the binder, onto the porous metal layer in the screen printing method.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Referring to the drawings, the basic construction of a PEM electrolyzer is represented in FIG. 1. The electrical voltage for creating hydrogen and oxygen from water is applied onto the outer bipolar plates 1 which comprise channels 2 for feeding the reactants of the water as well as for leading away the reaction products hydrogen and oxygen. The channels 2 of the bipolar plates 1 which are open to the inside of the electrolysis cell are covered by porous transport layers 3, 4 which are electrically conductive and liquid permeable. The porous transport layers 3 and 4 each bear on a catalyzer layer 5 and 6 respectively in an electrically conductive manner, said catalyzer layer being deposited onto a PEM 7. Concerning the electrolysis cell represented here for producing w hydrogen and oxygen from water, the anode-side transport layer 4 consists of titanium and the cathode-side transport layer 3 consists of graphite. The anode-side catalyzer layer 6 is formed from iridium oxide and the cathode-side catalyzer layer 5 of platinum. Such a construction is counted as belonging to the state of the art and is therefore not explained in detail.

[0040] Such an electrolysis cell is sealed off at the peripheral side, so that the necessary leading of fluid is ensured. A multitude of such electrolysis cells are arranged lying on one another as a stack (electrolysis stack), in order to form a powerful but compactly constructed electrolyzer. Hereinafter, the anode-side porous transport layer and its manufacturing method are explained, wherein this porous transport layer 4 can also serve for other electrochemical applications, and hence the application as an electrolyzer is cited only by way of example.

[0041] The porous transport layer 4 which is formed from titanium consists of a porous metal layer 8 in the form of a felt layer 8 which is formed from titanium fibers and which is gas permeable and conductive. This felt layer 8 is 0.25 mm thick and forms the carrier of the porous transport layer 4, on which a microporous metal layer 9 is deposited, said metal layer together with the metal layer 8 forming the anode-side porous transport layer 4 of titanium.

[0042] The microporous metal layer 9 which ensures the electrical connection between the porous transport layer 4 and the catalyzer layer 6 which bears thereon is effective on the one hand for the surfaced electrical connection of the bipolar plate 1 to the catalyzer layer 6 and on the other hand due to its micro-porosity ensures an intimate exchange of reactants as well as of the oxygen which is separated away at this side.

[0043] The microporous metal layer 9 is manufactured by way of fine metal powder, in this case titanium powder, with a maximum grain size of 10 μm being used with a binding agent for example of polyethylene and wax. Herein, the metal powder and the binder which is formed form polyethylene and wax are intensively mixed and granulated into a feedstock. This granulate is liquefied by way of an extruder and by way of a calender 11 is processed into a foil (an extensive element) 10 which has a thickness of 0.1 mm. This foil 10 forms the green part in this powder injection molding method and this foil 10 is shown in FIG. 3 in section and is subsequently deposited onto the porous metal layer 8, so that the arrangement which is evident from FIG. 4 results.

[0044] As the representation according to FIGS. 3 and 4 illustrate, the foil 10 consists of metal grains 12 which are encompassed by the binder 13 or are connected to one another by this. The porous metal layer 8 likewise consist of titanium and forms the carrier for the foil 10 which lies thereon. A release occurs in this arrangement, i.e. in a first thermal process the formation which consists of porous metal layer 8 and foil 10 is heated to such an extent that the binder 13 is removed and the metal grains 12 come to bear on the porous metal layer 8. The metal grains 12 now form a brown part which together with the porous metal layer 8 is subjected to a further heat treatment of a higher temperature (sintering), so that the metal grains 12 sinter amongst one another as well as to the porous metal layer, i.e. are unified and compacted into their final geometric and mechanical characteristic. Herein, a material-fit connection of the metal grains 12 as well as to the porous metal layer 8 takes place. This interconnection can also be formed by way of diffusion welding instead of by way of sintering. The thus formed porous transport layer 4 is formed by the porous metal layer 8 with the felt structure and the microporous metal layer 9 while lies thereabove. The latter is smoothed on its surface by way of rolling, so that a surface 14 as is represented schematically in FIG. 6 results. The surface smoothing can possibly be effected by way of grinding or by way of a combination of these machining methods. It serves for ensuring an as complete-surfaced as possible bearing contact of the thus formed porous transport layer 4 on the catalyzer layer 6.

[0045] In order to ensure an intimate interconnection and thus an electrically well conductive contact between the microporous metal layer 9 and the catalyzer layer 6, the surface 14 of the microporous metal layer 9, as is represented in FIG. 7, is microscopically roughened by way of pickling.

[0046] In the manufacturing method which are described above, a foil (extensive element) 10 consisting of metal grains 12 and binders 13 is manufactured as a green part in an injection molding method. Alternatively, this can be replaced by way of a foil (a extensive element) which is formed e.g. of polyethylene being used as a carrier foil which is provided with metal powder 12 and binder 13, wherein this foil (extensive element) which is provided with the metal powder—binder mixture is deposited onto the porous metal layer 8 instead of the foil (extensive element) 10 which is represented in FIG. 4. The further manufacturing method is effected as previously described.

[0047] An alternative manufacturing method for producing and depositing the microscopic layer 9 specifically in the screen printing method is represented by way of FIG. 8. There, a fabric 15 as a template is applied onto the porous metal layer 8 and instead of the otherwise deposited printing ink, here a pasty/fluid material 17 consisting of metal grains 12 and a binding agent are subsequently deposited by way of a doctor blade 16. After depositing the pasty material 17, the fabric 15 is removed and the pasty/fluid material 17 is brought into solidification by way of thermal action or e.g. evaporation of a solvent, wherein the consistency of the pasty/fluid material 17 is set such that a certain distribution is still effected after the removal of the fabric 15 so that an as homogeneous as possible smooth surface forms. Hereinafter, as with the initially described method, by way of a first thermal treatment the binding agent is then removed and subsequently by way of sintering or diffusion welding an interconnection of the metal grains 12 amongst one another as well as with the porous metal layer 8 is produced. The surface treatment steps can be effected as described above. Furthermore, the thermal removal of the binding agent can be replaced by a chemical removal or a combination of both.

[0048] Concerning the aforedescribed embodiment examples, the microporous metal layer 9 is continuously deposited on a porous metal layer 8, be it by way of applying a suitable foil 10 or a carrier foil which is provided with metal powder and binder or by way of a direct deposition of the mixture which is formed from the metal grains and the binder. As is represented by way of FIG. 4a, the porous metal layer 8 however can also be manufactured in an analogous manner as the microporous metal layer 9. It is to be understood that here a mixture of metal powder and binder is used, whose metal grains 12 are significantly larger than the metal grains 12 of the microporous metal layer and whose binder 13a can have the same composition or different composition than the binder 13. In FIG. 4a, a green part 8a of such a porous metal layer is represented, wherein this is machined together with the green part of the layer which lies above and which forms the later microporous metal layer 9, i.e. firstly the binder 13 and 13a is removed from both layers, so that a two-layered brown part which is formed from two brown parts results and this in the subsequent sintering procedure is sintered into the porous transport layer 4. This thus formed porous transport layer 4 is then usefully materially connected to the bipolar plate 1 e.g. by way of welding, so that an intrinsically stable, self-supporting component arises which in particular can be easily handled in an automated assembly process.

[0049] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.