As one of the critical components of a polymer electrolyte membrane (PEM) power stack, the commercial PEM stacks strongly depend on the durability and manufacturing cost of metallic bipolar plates. Therefore, hydrogen-free carbon-based nanocomposite coatings with a thickness of less than 500 nm were deposited on the low-cost AISI 316L austenitic stainless steel bipolar plates using pulsed direct current magnetron sputtering in the present work. The developed hydrogen-free carbon-based nanocomposite coatings, particularly Ti/TiCN/C, Cr/(CrCN/TiCN)₆/C and Cr/(CrCN/C)₃/C, exhibit a smooth, uniform and dense microstructure, which is of critical importance in enhancing the overall efficiency and stability of the power stack. The hardness (H), H/E* and H³/E*² of the aforementioned coatings are 12.4 –2 0.45 GPa, 0.088 – 0.097 and 0.097 – 0.194, respectively. The interface contact resistance is 2.4 – 2.7 mΩ · cm² @ 0.6 MPa. In the acidic medium (PH = 3, H₂SO₄ + 0.1 ppm HF), the corrosion behavior is dominated by homogeneous corrosion. The corrosion current density and the corrosion voltage under potentiodynamic polarization are 3.74 – 41.8×10^-8 A · cm^-2 and -223 – -20.6 mV, respectively. The corrosion current density is determined to be 2.58 – 16.1×10^-8 A · cm^-2 under potentiostatic polarization at 0.84 V for 24 h. The contact angles of the as-deposited and corroded coatings in potentiodynamic polarization are observed to be 30.4^o – 39.3^o and 37.5^o – 47.2^o, respectively. The dense, multilayered interfaces and top hydrogen-free carbon layers contributed to a combined improvement in the obdurability, electrical conductivity and corrosion resistance of hydrogen-free carbon-based nanocomposite coatings.
 

Hydrogen-free carboned nanocomposite coating, Stainless steel bipolar plate, Electrical conductivity, Corrosion resistance, Contact angle