Nanotube assembly, bipolar plate and process of making the same
One embodiment of the invention includes an assembly of metal oxide comprising valve metal oxide nanotubes.
1. A method of making a metal oxide nanotube assembly comprising:
providing a substrate comprising stainless steel;
providing a valve metal on the substrate, the valve metal comprising at least one of titanium, zirconium, niobium, tantalum, hafnium or alloys or mixtures thereof;
anodizing said valve metal in an electrolyte solution to cause the formation of a nanotube assembly on the valve metal surface and so that nanotubes of the nanotube assembly have an average diameter of 60-75 nm and a length ranging from 15-300 nm; and
passivating said valve metal in an electrolyte solution at an anodizing potential or voltage such that the electric current flowing through the valve metal reaches a minimum level and the valve metal is corrosion resistant.
2. A method as set forth in claim 1 further comprising rinsing said valve metal to remove electrolyte solution.
3. A method as set forth in claim 1 wherein the anodizing further causing the surface to be roughened before the formation of a nanotube assembly.
4. A method as set forth in claim 1 , wherein said valve metal is titanium.
5. A method as set forth in claim 1 , wherein said electrolyte solution comprises an ion comprising at least one of chloride, fluoride, or cyanide.
6. A method as set forth in claim 1 , wherein said electrolyte solution comprises at least one of hydrogen fluoride or a fluoride salt.
7. A method as set forth in claim 1 wherein the providing the valve metal on a substrate comprises cladding a thin foil of the valve metal on the substrate.
8. A method as set forth in claim 1 wherein the providing the valve metal on a substrate comprises depositing a thin layer of the valve metal on the substrate by physical vapor deposition.
9. A method as set forth in claim 1 further comprising calcinating the assembly of nanotube at a temperature ranging from 300-700 degrees Celsius to produce an anatase rich crystalline form of titanium nanotubes in the nanotube assembly.
10. A method as set forth in claim 1 wherein the electrolyte solution include hydrogen fluoride.
11. A method of making a metal oxide nanotube assembly comprising:
providing a valve metal comprising at least one of titanium, zirconium, niobium, tantalum, hafnium or alloys or mixtures thereof;
anodizing said valve metal in an electrolyte solution to cause the formation of a nanotube assembly on the valve metal surface; and
passivating said valve metal in an electrolyte solution at an anodizing potential or voltage such that the electric current flowing through the valve metal reaches a minimum level and the valve metal is corrosion resistant;
wherein the valve metal is a fuel cell bipolar plate having a reactant gas flow field defined in at least one face thereon, the flow field being defined by a plurality of lands and channels.
12. A method of making a metal oxide nanotube assembly comprising:
providing a substrate comprising stainless steel;
providing a valve metal on the substrate comprising at least one of titanium, zirconium, niobium, tantalum, hafnium or alloys or mixtures thereof;
anodizing said valve metal in an electrolyte solution to cause the formation of a nanotube assembly on the valve metal surface; and
passivating said valve metal in an electrolyte solution at an anodizing potential or voltage such that the electric current flowing through the valve metal reaches a minimum level and the valve metal is corrosion resistant;
further comprising depositing a conductive coating on said nanotube assembly to provide a contact resistance of about 50 milli-ohms/cm 2 or less, and said conductive coating comprising a carbon, ruthenium oxide, rhodium oxide, platinum oxide, palladium oxide, osmium oxide, or iridium oxide.
13. A method of making a metal oxide nanotube assembly comprising:
providing a substrate comprising stainless steel;
providing a valve metal on the substrate comprising at least one of titanium, zirconium, niobium, tantalum, hafnium or alloys or mixtures thereof;
anodizing said valve metal in an electrolyte solution to cause the formation of a nanotube assembly on the valve metal surface; and
passivating said valve metal in an electrolyte solution at an anodizing potential or voltage such that the electric current flowing through the valve metal reaches a minimum level and the valve metal is corrosion resistant.