Gas diffusion electrodes, membrane-electrode assemblies and method for the production thereof
A method for forming a mixed metal coating on a gas diffusion medium substantially free of ionomeric components which includes the steps of subjecting an electrically conductive web to a first ion beam having an energy not higher than 500 eV, then to a second beam having an energy of at least 500 eV containing the ions of a first metal, and to at least a third beam having an energy of at least 500 eV containing the ions of a noble metal. The invention also relates to gas diffusion electrodes.
1. A method for forming a mixed metal coating on a gas diffusion medium substantially free of ionomeric components which comprises subjecting an electrically conductive web to a first ion beam having an energy not higher than 500 eV, then to a second beam having an energy of at least 500 eV containing the ions of a first metal, and to at least a third beam having an energy of at least 500 eV containing the ions of a noble metal and wherein said first metal is cobalt or chromium and wherein the mixed metal coating is two overlaid layers of two different, distinct metals and is deposited on the gas diffusion medium which is substantially free of ionomeric components.
2. The method of claim 1 , wherein prior to subjecting said electrically conductive web to said ion beams, a patterned mask is overlaid thereto to obtain a patterned mixed metal coating.
3. The method of claim 2 , wherein said patterned mask is a thin metal sheet or polymer film provided with holes.
4. The method of claim 2 , wherein said patterned mask is a chemically etched, thin metal sheet.
5. The method of claim 3 , wherein the distance between the centers in adjacent couples of said holes is between 0.02 and 0.5 cm.
6. The method of claim 2 , wherein said patterned mask has an open ratio between 30 and 80%.
7. The method of claim 2 , wherein said patterned mask is a polygonal grid.
8. The method of claim 7 , wherein said polygonal grid comprises equally spaced polygonal holes, with a circular filled center, and the resulting patterned noble metal coating is comprised of equally spaced polygons, having a round hole center.
9. The method of claim 1 , wherein the mixed metal coating has a total thickness between 5 and 250 nm and a loading of 0.01 to 0.3 mg/cm2.
10. The method of claim 1 , wherein said first ion beam has an energy between 100 and 500 eV and said second and third ion beams have an energy between 500 and 2000 eV.
11. The method of claim 1 wherein the noble metal is platinum.
12. The method of claim 8 wherein said polygons are hexagons.