Stainless separator for fuel cell and method of manufacturing the same
A stainless steel separator for fuel cells and a method of manufacturing the same are disclosed. The method includes preparing a stainless steel sheet as a matrix, performing surface modification on a surface of the stainless steel sheet to form a Cr-rich passive film having a comparatively increased amount of Cr in a superficial layer of the stainless steel sheet by decreasing an amount of Fe in the superficial layer of the stainless steel sheet, and forming a coating layer on the surface of the surface-modified stainless steel sheet. The coating layer is one selected from a metal nitride layer (MN x ), a metal/metal nitride layer (M/MN x ), a metal carbide layer (MC y ), and a metal boride layer (MB z ) (where 0.5≦x≦1, 0.42≦y≦1, 0.5≦z≦2).
1. A method of manufacturing a stainless steel separator for fuel cells, the method comprising:
preparing a stainless steel sheet as a matrix;
performing surface modification on a surface of the stainless steel sheet to form a Cr-rich passive film having a comparatively increased amount of Cr in a superficial layer of the stainless steel sheet by decreasing an amount of Fe in the superficial layer of the stainless steel sheet; and
forming a coating layer on the surface of the surface-modified stainless steel sheet, wherein the coating layer is a metal boride layer (MBz), and 0.5≦z≦2.
2. The method according to claim 1 , wherein the metal (M) used in the forming a coating layer is at least one selected from chromium (Cr), titanium (Ti), zirconium (Zr), and tungsten (W).
3. The method according to claim 1 , wherein the metal (M) used in the forming a coating layer is selected from transition metals.
4. The method according to claim 1 , wherein the Cr-rich passive film constituting the superficial layer of the stainless steel sheet has a (Cr+Ni)/Fe ratio of 1 or more in terms of atomic weight ratio.
5. The method according to claim 1 , wherein the coating layer is formed in a film shape having a thickness of 30˜300 nm.
6. The method according to claim 1 , wherein the surface modification comprises immersing the stainless steel sheet in a solution comprising sulfuric acid (H2SO4) and nitric acid (HNO3), or spraying the solution onto the surface of the stainless steel sheet.
7. The method according to claim 6 , wherein the surface modification solution further comprises one or more additives selected from hydrogen peroxide (H2O2) and oxalic acid (C2H2O4).
8. The method according to claim 1 , wherein the surface modification comprises immersing the stainless steel sheet in a surface modification solution comprising sulfuric acid (H2SO4), and applying a potential (or current) in an SHE region of greater than 0 to 1.0V.
9. The method according to claim 1 , wherein the coating layer is formed by sputtering or arc ion plating.
10. The method according to claim 9 , wherein the sputtering is reactive sputtering.
11. The method according to claim 1 , wherein the stainless steel sheet contains 16˜28 wt % chromium.