Stainless steel separator for fuel cell having M/MN
Disclosed herein is a stainless steel separator for a fuel cell and method of manufacture. The stainless steel separator includes a stainless steel sheet, a first coating layer comprising metal/metal nitride films (M/MN x ) (0.5≦x≦1) on a surface of the stainless steel sheet, and a second coating layer comprising a metal oxynitride film (MO y N z ) (0.05≦y≦2, 0.25≦z≦1.0).
1. A stainless steel separator for a fuel cell comprising:
a stainless steel sheet extending in one plane along one axis;
a first coating layer composed of a plurality of metal/metal nitride films (M/MNx) (0.5≦x≦1) on a surface of the stainless steel sheet; and
a second coating layer comprising a metal oxynitride film (MOyNz) (0.05≦y≦2, 0.25≦z≦1.0) formed on the first coating layer,
wherein the metal oxynitride film of the second coating layer has an increasing oxygen concentration towards the surface of the first coating layer.
2. The stainless steel separator according to claim 1 further comprising:
a passive film interposed between the surface of the stainless steel sheet and the first coating layer.
3. The stainless steel separator according to claim 1 , wherein the metal/metal nitride films of the first coating layer comprises the metal film (M) contacting the stainless steel sheet and the metal nitride film (MN) contacting the second coating layer.
4. The stainless steel separator according to claim 1 , wherein the metal (M) in the first coating layer and the second coating layer is selected from the group consisting of chrome (Cr), titanium (Ti), and zirconium (Zr).
5. The stainless steel separator according to claim 1 , wherein the metal (M) in the first coating layer and the second coating layer is selected from the group consisting of transition metals.
6. The stainless steel separator according to claim 1 , wherein the plurality of metal/metal nitride films comprise Cr/CrN films.
7. The stainless steel separator according to claim 6 , wherein a number of the plurality of chrome/chrome nitride (Cr/CrN) films is 2-200.
8. The stainless steel separator according to claim 1 , wherein the metal oxynitride film comprises CrOyNz (0.05≦y≦2, 0.25≦z≦1.0).
9. The stainless steel separator according to claim 1 , wherein the second coating layer has a thickness of 10-100 nm.
10. The stainless steel separator according to claim 1 , wherein when the second coating layer has a thickness of 100 nm, an atomic ratio of [O/N] at a depth of 5-15 nm from a surface of the second coating layer is 0.2-8.
11. The stainless steel separator according to claim 1 , wherein when the second coating layer has a thickness of 100 nm, an atomic ratio of [O/N] at a depth of 45-55 nm from a surface of the second coating layer is 0.5 or less.
12. A method of manufacturing the stainless steel separator for the fuel cell according to claim 1 by sputtering, comprising:
performing sputtering with a metal target in an argon atmosphere to form a metal film of a first coating layer;
performing sputtering in a combined argon-nitrogen atmosphere to form a metal nitride film of the first coating layer (when forming the first coating layer comprising multiple metal/metal nitride films (M/MN), repeating the sputtering while alternating between the argon atmosphere and the combined argon-nitrogen atmosphere); and
performing sputtering in a combined nitrogen-oxygen atmosphere to form a second coating layer comprising a metal oxynitride film (MOyNz) (0.05≦y≦2, 0.25≦z≦1.0) on the first coating layer.
13. The method according to claim 12 , wherein the metal (M) in the first coating layer and the second coating layer is at least one selected from chrome (Cr), titanium (Ti), and zirconium (Zr).
14. The method according to claim 12 wherein the metal (M) in the first coating layer and the second coating layer is one selected from transition metals.
15. The method according to claim 12 , wherein the sputtering is performed by a reactive sputtering process.