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-----Chemically stable and highly conductive metal films
I am working in the fuel cell area and am trying to develop a lightweight current collector on silicon substrates by depositing thin conductive films of copper (2-5um) onto the substrates and then sputter or e-beam coating with a precious metal such as gold or platinum to protect the copper from corrosion but still have a highly conductive coating. I have found that in a fuel cell environment where sulfuric acid in the liquid state is present, that the pinholes in the gold and or platinum allow the underlying copper to be corroded and dissolved which then causes a "shark skin" appearance to the precious metal film and delamination from the silicon. I know that silver is a better conductor than copper and has a much higher corrosion resistance but I do not know if silver can be used to replace the copper and then coated with gold or platinum or any other inert conductor for that matter to maintain high conductivity and chemical resistance to dilute sulfuric acid solutions! . Any suggestions?
Larry J. Markoskifuel cell developer - Champaign, Illinois, USA
2004
2004
There are a few different issues here. One is that the copper and gold or silver and gold will interdiffuse over time (rapidly if hot), so you can't maintain that gold coating. A layer of nickel plating in between will solve that problem, but I don't know the practicality of plating this object. Having done that, though, you can use a nitric acid or nitric fume porosity test to insure the gold is pore-free.
Another possibility if the geometry is complex, would be to follow the copper with electroless nickel, and possibly electroless gold or immersion gold plating.
Ted Mooney, P.E.
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