Fuel Cell Assembly and Method for Operating a Fuel Cell Assembly

Abstract

A fuel cell assembly with at least one PEM fuel cell for generating electrical energy from reactant gases includes at least one membrane/electrode having a membrane coated with platinum electrodes and, respectively positioned on each side, a porous gas diffusion layer, or having a membrane and, respectively positioned on each side, a porous gas diffusion layer coated with a platinum electrode, and also includes bipolar plates that lie against the gas diffusion layers and through which, during operation, a coolant flows, wherein at least one of the platinum electrodes has a smaller area than the gas diffusion layer, where the gas diffusion layer protrudes beyond the platinum electrode for a part of an edge region of the membrane/electrode unit, so that the formation of an electrochemical potential in this part of the edge region of the membrane/electrode unit is prevented in order to prevent damage to the membrane.

Claims

1.-8. (canceled)

9. A fuel cell assembly with at least one proton exchange membrane fuel cell for generating electrical energy from reactant gases comprising hydrogen and oxygen, comprising: at least one membrane/electrode unit having a membrane coated with platinum electrodes and having, respectively positioned on each side thereof, a porous gas diffusion layer; bipolar plates which lie against each porous diffusion layer and through which, during operation, a coolant flows; wherein at least one platinum electrode has a smaller area than the gas diffusion layer; wherein the gas diffusion layer protrudes beyond the platinum electrode for a part of an edge region of the membrane/electrode unit and the gas diffusion layer does not protrude beyond the platinum electrode for another part of the edge region of the membrane/electrode unit; and wherein the edge region is a region around an outer periphery of the membrane/electrode unit.

10. The fuel cell as claimed in claim 9, wherein the protrusion of the gas diffusion layer beyond the platinum electrode is provided in one of (i) at a region of a coolant exit from the bipolar plate and (ii) at thermally loaded sites of the bipolar plate.

11. The fuel cell as claimed in claim 9, wherein access by at least one of the reactant gases comprising hydrogen and oxygen to the membrane is blocked by a mechanical block disposed between the gas diffusion layer and the membrane in a region of the protrusion.

12. The fuel cell as claimed in claim 11, wherein the mechanical block comprises a gas-impermeable film.

13. The fuel cell as claimed in claim 11, wherein the mechanical block is contained within pores of the gas diffusion layer.

14. The fuel cell as claimed in claim 13, wherein the mechanical block comprises one of (i) an acrylic adhesive and (ii) a fluorothermoplastic.

15. The fuel cell assembly with at least one proton exchange membrane fuel cell for generating electrical energy from the reactant gases hydrogen and oxygen, comprising: at least one membrane/electrode unit having a membrane and, respectively positioned on each side thereof, a porous gas diffusion layer coated with a platinum electrode; bipolar plates which lie against each gas diffusion layer and through which, during operation, a coolant flows; wherein at least one platinum electrode has a smaller area than the gas diffusion layer; wherein the gas diffusion layer protrudes beyond the platinum electrode for a part of an edge region of the membrane/electrode unit and the gas diffusion layer does not protrude beyond the platinum electrode for another part of the edge region of the membrane/electrode unit; and wherein the edge region is a region around an outer periphery of the membrane/electrode unit.

16. The fuel cell as claimed in claim 15, wherein the protrusion of the gas diffusion layer beyond the platinum electrode is provided in one of (i) at a region of a coolant exit from the bipolar plate and (ii) at thermally loaded sites of the bipolar plate.

17. The fuel cell as claimed in claim 15, wherein access by at least one of the reactant gases comprising hydrogen and oxygen to the membrane is blocked by a mechanical block disposed between the gas diffusion layer and the membrane in a region of the protrusion.

18. The fuel cell as claimed in claim 16, wherein access by at least one of the reactant gases comprising hydrogen and oxygen to the membrane is blocked by a mechanical block disposed between the gas diffusion layer and the membrane in a region of the protrusion.

19. The fuel cell as claimed in claim 17, wherein the mechanical block comprises a gas-impermeable film.

20. The fuel cell as claimed in claim 17, wherein the mechanical block is contained within pores of the gas diffusion layer.

21. The fuel cell as claimed in claim 20, wherein the mechanical block comprises one of (i) an acrylic adhesive and (ii) a fluorothermoplastic.

22. A method for operating a fuel cell assembly with at least one proton exchange membrane fuel cell for generating electrical energy from the reactant gases hydrogen and oxygen, the method comprising: recessing a platinum electrode and protruding a gas diffusion layer beyond the platinum electrode such that formation of an electrical potential in this part of an edge region of a membrane/electrode unit is prevented for a part of the edge region of the membrane/electrode unit; and ensuring the platinum electrode is not recessed and ensuring the gas diffusion layer does not protrude beyond the platinum electrode such that formation of an electrochemical potential in this part of the edge region of the membrane/electrode unit is not prevented for another part of the edge region of the membrane/electrode unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] An exemplary embodiment of the invention will now be described in greater detail making reference to the figures, in which:

[0023] FIG. 1 is a first plan view of a membrane/electrode unit and a gas diffusion layer lying thereon where a first, exemplary, critical region is identified;

[0024] FIG. 2 is a second plan view of a membrane/electrode unit and a gas diffusion layer lying thereon where a second, exemplary, critical region is identified;

[0025] FIG. 3 is a cross-section of a first embodiment of a fuel cell in accordance with the invention;

[0026] FIG. 4 is a cross-section of a second embodiment of a fuel cell in accordance with the invention;

[0027] FIG. 5 is a cross-section of a third embodiment of a fuel cell in accordance with the invention; and

[0028] FIG. 6 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0029] The same reference signs have the same meaning in the different figures.

[0030] Shown in FIGS. 1 and 2, respectively, is a membrane/electrode unit 2 that is part of a fuel cell assembly 3 (not shown here in detail) that consists in the illustrated exemplary embodiment of a single proton exchange membrane (PEM) fuel cell. The PEM fuel cell 3 is shown in cross-section in FIGS. 3 to 5.

[0031] The membrane/electrode unit 2 comprises a proton-conducting membrane 4 that is coated on both sides with a catalyst layer of platinum (not shown here) that forms a platinum electrode 5 (see, e.g., FIGS. 3 to 5). Placed on each side of the membrane 4 is a gas diffusion layer 6, which contacts the platinum electrode 5. Alternatively, the catalyst layer of platinum that forms a platinum electrode 5 can also be applied to the gas diffusion layer 6 on the side facing toward the membrane 4.

[0032] As shown in FIGS. 3 to 5, the fuel cell 3 also comprises, adjoining the gas diffusion layer 6, a bipolar plate 7 (in reality, a space is at least partially present between the bipolar plate 7 and the gas diffusion layer 6) through which, during operation a coolant, i.e., cooling water, flows. With this, heat generated in the membrane/electrode unit 2 is transported away.

[0033] In FIGS. 1 and 2, reference sign 8 denotes two differently arranged exemplary critical sites at which there is an increased probability that a disruption of the function of the membrane 6 or a local destruction of the membrane 6 can occur. For example, such a critical site 8 is at the coolant exit from the bipolar plate 7, as shown in FIG. 1. The critical sites 8 are always located in the edge region of the membrane/electrode unit 2 or the gas diffusion layer 6.

[0034] The edge region is herein understood to be the region around the outer periphery of the membrane/electrode unit 2.

[0035] In FIG. 3, a first arrangement of the fuel cell 3 is shown in which, at a critical site 8 in the edge region, the platinum electrodes 5 are recessed, so that for this part of the edge region, the gas diffusion layer 6 protrudes beyond the platinum electrode 5. With this, the platinum electrodes 5 have a smaller area than the gas diffusion layer 6. In this way, formation of an electrochemical potential forms at the critical site 8 is prevented.

[0036] In FIG. 4 also, the platinum electrode 5 is also recessed, with the difference from FIG. 3 being that a film-like mechanical block 10 in the manner of a film is provided between the membrane 4 and the gas diffusion layer 6. At the critical site 8, the platinum electrode 5 is thus replaced by the film 10.

[0037] In FIG. 5, a third alternative embodiment of the fuel cell 3 is shown, where the porous gas diffusion layer 6 is filled with the mechanical block 10, specifically only in the region of the critical site 8, where the platinum electrode 5 is omitted. The mechanical block 10 is herein a mass, such as a thermoplastic, fluorinated polymer filler or an acrylic adhesive.

[0038] FIG. 6 is a flowchart of a method for operating a fuel cell assembly 3 with at least one proton exchange membrane (PEM) fuel cell for generating electrical energy from the reactant gases hydrogen and oxygen. The method comprises recessing a platinum electrode 5 and protruding a gas diffusion layer 6 beyond the platinum electrode 5 such that formation of an electrical potential in this part of an edge region of the membrane/electrode unit 2 is prevented for a part of the edge region of the membrane/electrode unit 2, as indicated in step 610. Next, the platinum electrode 5 is not recessed and ensuring the gas diffusion layer 6 is arranged to not protrude beyond the platinum electrode 5 such that formation of an electrochemical potential in this part of the edge region of the membrane/electrode unit 2 is not prevented for another part of the edge region of the membrane/electrode unit 2, as indicated in step 620.

[0039] While there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.