Fuel cell assembly and method for operating a fuel cell assembly
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.
1. 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 at a region of a coolant exit from a bipolar plate 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 another edge region of the membrane/electrode unit.
2. 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 of the platinum electrodes has a smaller area than the gas diffusion layer;
wherein the gas diffusion layer protrudes beyond the at least one platinum electrode for a part of an edge region of the membrane/electrode unit and the gas diffusion layer does not protrude beyond the at least one platinum electrode for another part of the edge region of the membrane/electrode unit;
wherein the edge region is a region around an outer periphery of the membrane/electrode unit; and
wherein the protrusion of the gas diffusion layer beyond the platinum electrode is provided at a region of a coolant exit from the bipolar plates.
3. The fuel cell as claimed in claim 2 , 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.
4. The fuel cell as claimed in claim 3 , wherein the mechanical block comprises a gas-impermeable film.
5. The fuel cell as claimed in claim 3 , wherein the mechanical block is contained within pores of the gas diffusion layer.
6. The fuel cell as claimed in claim 5 , wherein the mechanical block comprises one of (i) an acrylic adhesive and (ii) a fluorothermoplastic.
7. A 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 the 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;
wherein the edge region is a region around an outer periphery of the membrane/electrode unit; and
wherein the protrusion of the gas diffusion layer beyond the platinum electrode is provided at a region of a coolant exit from the bipolar plate.
8. The fuel cell as claimed in claim 7 , 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.
9. The fuel cell as claimed in claim 7 , 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.
10. The fuel cell as claimed in claim 8 , wherein the mechanical block comprises a gas-impermeable film.
11. The fuel cell as claimed in claim 8 , wherein the mechanical block is contained within pores of the gas diffusion layer.
12. The fuel cell as claimed in claim 11 , wherein the mechanical block comprises one of (i) an acrylic adhesive and (ii) a fluorothermoplastic.