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;
heat-treating the surface-modified stainless steel sheet at 100˜300° C. under a vacuum condition; and
forming a coating layer directly on the heat-treated stainless steel sheet,
wherein the coating layer is a metal boride layer (MBz), and
wherein 0.5≦z≦2.
2. The method according to claim 1 , wherein the heat-treating is performed at a temperature of 100˜200° C.
3. 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.
4. The method according to claim 1 , wherein the heat-treating is performed for 3 minutes to 1 hour.
5. The method according to claim 1 , wherein the surface modification comprises immersing the stainless steel sheet in a solution comprising sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ), or spraying the solution onto the surface of the stainless steel sheet.
6. The method according to claim 5 , wherein the surface modification solution further comprises one or more additives selected from hydrogen peroxide (H 2 O 2 ) and oxalic acid (C 2 H 2 O 4 ).
7. The method according to claim 1 , wherein the surface modification comprises immersing the stainless steel sheet in a surface modification solution comprising sulfuric acid (H 2 SO 4 ), and applying a potential or current in an SHE region of greater than 0 to 1.0V.
8. The method according to claim 1 , wherein the heat-treating is selectively performed by one of batch type heat treatment and continuous line heat treatment.
9. The method according to claim 1 , wherein the stainless steel sheet contains 16-28 wt % chromium.