Gas diffusion electrodes, membrane-electrode assemblies and method for the production thereof
A method for forming a patterned noble metal coating on a gas diffusion medium substantially free of ionomeric components comprising subjecting an electrically conductive web with a patterned mask overlaid thereto to a first ion beam having an energy not higher than 500 eV, and to a second beam having an energy of at least 500 eV, containing the ions of at least one noble metal and a gas diffusion electrode.
1. A method for forming a patterned noble metal coating on a gas diffusion medium substantially free of ionomeric components comprising subjecting an electrically conductive web with a patterned mask overlaid thereto to a first ion beam having an energy not higher than 500 eV, and to a second beam having an energy of at least 500 eV, containing the ions of at least one noble metal.
2. The method of claim 1 wherein said patterned mask is a thin metal sheet or polymer film provided with holes.
3. The method of claim 2 wherein said thin patterned mask is chemically etched thin metal sheet.
4. The method of claim 2 wherein the distance between the centers in adjacent couples of said holes is between 0.02 and 0.5 cm.
5. The method of claim 1 wherein said patterned mask has an open ratio between 30 and 80%.
6. The method of claim 1 wherein said patterned mask is a polygonal grid.
7. The method of claim 6 wherein said polygonal grid comprises equally spaced polygonal holes, optionally hexagonal holes, with a circular filled center, and the resulting patterned noble metal coating is comprised of equally spaced polygons, optionally hexagons, having a round hole center.
8. The method of claim 1 , wherein the patterned noble metal coating has a thickness between 5 and 250 nm and a loading of 0.01 to 0.3 mg/cm 2 .
9. The method of claim 1 wherein said first ion beam has an energy comprised between 100 and 500 eV and said second ion beam has an energy comprised between 500 and 2000 eV.
10. The method of claim 1 wherein said at least one noble metal is platinum.
11. A gas diffusion electrode comprising an electrically conductive web, a non catalyzed gas diffusion layer comprising at least one electroconductive filler and at least one optionally fluorinated binder, and a patterned noble metal coating obtained by the method of claim 1 .
12. The gas diffusion electrode of claim 11 wherein said electroconductive filler comprises carbon particles.
13. The gas diffusion electrode of claim 11 wherein the electroconductive filler is acetylene black carbon particles.
14. The gas diffusion electrode of claim 12 wherein said gas diffusion layer has a smoothness of at least 1000 Gurley-seconds.
15. A member-electrode assembly comprising at least one gas diffusion electrode of claim 11 and an ion-exchange membrane.
16. The membrane-electrode assembly of claim 14 wherein said at least one gas diffusion electrode and said ion-exchange membrane are mutually bonded by hot pressing.