The enhanced conductivity and corrosion resistance of hydrogen-free carbon-based nanocomposite coatings

Synergistic optimization of conductivity and corrosion resistance in metallic bipolar plates (BPs) is crucial for improving the performance, reliability, and longevity of proton exchange membrane fuel cell (PEMFC) systems. In this study, three hydrogen-free carbon-based nanocomposite coatings (Cr, Ti)/(Cr, Ti)-C-N/C were deposited on AISI austenitic stainless steel (SS316L) BPs using pulsed DC magnetron sputtering. The Ti/TiCN/C coatings demonstrate superior performance, characterized by smooth, uniform, and dense microstructure comprising Ti adhesion layer, TiCN transition layer and top C layer. The Ti/TiCN/C coatings demonstrate the highest hardness (21.36 GPa), the largest H/E∗ (0.072) and H³/E∗² (0.084) ratios, maximum coating-substrate adhesion (20.3 mN), and excellent corrosion resistance in acidic conditions (pH = 3, H₂SO₄ + 0.1 ppm HF, 80 °C). Enhanced performances stem from the microstructural uniformity, strong interfacial bonding, and the regulating effect of the intermediate transition layer on the top C layer. Additionally, the Ti/TiCN/C coatings achieve the lowest interfacial contact resistance value of 2.4 mΩ·cm², which is attributed to the maximum content and degree of disorder of C sp², and the highest sp²/sp³ ratio in the top C layer. These results highlight Ti/TiCN/C coatings as a cost-effective, durable solution for high-performance PEMFC BPs, thereby offering a foundation for industrial-scale applications.