Improved Corrosion Resistance and Interfacial Conductivity of A-C/(ti:C)/ti Nano-Thin Film for 316L Stainless Steel Bipolar Plates

To enhance corrosion resistance and electrical conductivity of metallic bipolar plates for proton exchange membrane fuel cells (PEMFCs), the film containing amorphous carbon (a-C) outer layer, titanium carbon compound (Ti:C) transition layer and titanium (Ti) seed layer has been deposited on the surface of 316L stainless steel (316L SS) by multi-arc ion plating method. Dense and uniform a-C/(Ti:C)/Ti nano-thin film is relatively hydrophobic and approximately 300 nm thick, presenting a clear multilayer structure. The interfacial contact resistance of 316L SS is effectively reduced from 124.97 mΩ·cm2 to 3.97 mΩ·cm2 at 1.4 MPa after modification. Electrochemical corrosion tests are investigated in the simulated cathodic PEMFCs environment (0.5 M H2SO4 and 2 ppm HF at 70 ℃ bubbled with air). Potentiodynamic polarization results reveal that the corrosion potential of a-C/(Ti:C)/Ti film modified sample is 0.23 V (vs. Ag/AgCl) and the corrosion current density is only 0.14 μA·cm−2. The durability of the a-C/(Ti:C)/Ti films was assessed by conducting potentiostatic polarization tests at various applied potentials. After 4 hours potential of 0.6 V and 0.8 V (vs Ag/AgCl) holding tests, the current densities of the modified 316L SS have stabilized at 0.076 μA·cm−2 and 0.098 μA·cm−2, respectively.