Diamond‐Like‐Carbon Coated Metallic Bipolar Plates for PEM Fuel Cells: An Assessment of Coating Thickness Effect

ABSTRACT Metallic bipolar plates are key to low‐cost compact stack design for proton exchange membrane (PEM) fuel cells, but suffer serious surface corrosion and require surface protective coatings such as diamond‐like‐carbon (DLC). In this study, the impact of DLC coating thickness on the corrosion characteristics of SS316L bipolar plates is investigated in an ex‐situ environment simulating the operating environment in PEM fuel cells, and three coating thicknesses of 47, 100, and 197 nm are evaluated for their surface morphology, composition, corrosion resistance, wettability, and interfacial contact resistance. x‐Ray photoelectron spectroscopy measurements reveal the sp 2 (graphite‐like) to sp 3 (diamond‐like) hybridization ratio, while scanning electron microscopy results show dense coating layer structures. Corrosion resistance is assessed using potentiostatic and potentiodynamic polarizations and electrochemical impedance spectroscopy (EIS) in a simulated fuel cell environment with 1 M H 2 SO 4 at 80°C. It is found that all coated samples meet the US Department of Energy (DOE) targets for corrosion resistance, and the 100 nm thick DLC coating shows the best performance, with the lowest corrosion current density (0.110 µA/cm 2 ), highest corrosion potential (17.31 mV), and highest resistance to charge transfer (5.36·10 6 Ω cm 2 ); and maintain hydrophobicity (contact angle of 92° and surface free energy of 17.00 mJ/m 2 ) after 5 h of potentiostatic polarization, suggesting excellent potential for water management and corrosion resistance. Further, these coated samples meet the DOE targets for interfacial contact resistance of < 10 mΩ cm 2 . Therefore, the 100 nm thick DLC coating demonstrates superior anticorrosion performance required for PEM fuel cell applications.