Factors Affecting the Formation of Carbon Film on the Stainless Steels for the Bipolar Plate of Polymer Electrolyte Fuel Cells

Factors affecting the formation of carbon film by plasma-assisted chemical vapor deposition on stainless steels were investigated in detail. When the carbon coating time increased, the morphology and crystallinity of the formed carbon changed. The depth profile of the resulting carbon coated sample indicated that it was consisted of top carbon layer without metal species and interfacial layer mainly containing chromium oxide and carbon of lower crystallinity. The top carbon layer with the morphology similar to that of carbon nanowall effectively covered the surface of the metal substrate, providing the high electrochemical stability in an acidic solution. As the cold working rate of the stainless steel substrate increases, the time needed for the complete coverage of the metal surface became shorter. Based on the scanning electron microscopy observation and X-ray diffraction, this was mainly ascribed to the increase in defects where the nucleus formation of carbon can occur and the increased density of carbon on the surface of the metal. The resulting carbon coated stainless steels showed low interfacial resistance and high corrosion resistance in acidic solution even at $80°C$⁠, and is promising for the bipolar plate of polymer electrolyte fuel cells.