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 stainless steel separator for fuel cells, comprising:
a stainless steel sheet having a matrix structure;
a Cr-rich passive film directly formed on a surface of the stainless steel sheet, and containing 20˜75 wt % chromium; and
a coating layer disposed directly on the Cr-rich passive film, and having a thickness of 30˜300 nm,
wherein the coating layer is a metal boride layer (MB z ), and
wherein 0.5≦z≦2.
2. The stainless steel separator according to claim 1 , wherein the coating layer is a continuous film disposed on the passive film.
3. The stainless steel separator according to claim 1 , wherein the metal (M) of the coating layer is at least one selected from chromium (Cr), titanium (Ti), zirconium (Zr), and tungsten (W).
4. The stainless steel separator according to claim 1 , wherein the passive film has a (Cr+Ni)/Fe ratio of 1 or more in terms of atomic weight ratio.
5. The stainless steel separator according to claim 1 , wherein the stainless steel sheet comprises 0.08 wt % or less carbon (C), 16˜28 wt % chromium (Cr), 0.1˜20 wt % nickel (Ni), 0.1˜6 wt % molybdenum (Mo), 0.1˜5 wt % tungsten (W), 0.1˜2 wt % tin (Sn), 0.1˜2 wt % copper (Cu), and the balance of iron (Fe) and unavoidable impurities.
6. The stainless steel separator according to claim 1 , wherein the stainless steel separator has a corrosion current density less than 1 μA/cm 2 and a contact resistance less than 20 mΩ·cm 2 on both surfaces thereof.