Optimizing pH-dependent electrochemical performance: corrosion resistance and conductivity tailoring in C/Ti/SS composite coatings on SS316L for PEMFC bipolar plates

Purpose This study aims to develop a high-performance C/Ti/SS composite coating via pulsed bias arc ion plating (PBAIP) to enhance conductivity and corrosion resistance of SS316L bipolar plates in PEMFC applications while investigating the pH-dependent degradation mechanisms under simulated fuel cell operating conditions. Design/methodology/approach The C/Ti/SS composite coatings were fabricated on SS316L substrates using PBAIP, sequentially depositing a corrosion-resistant Ti interlayer and a conductive C top layer. The coatings were systematically evaluated in simulated PEMFC environments (0.5 M H2SO4 + 2 ppm HF, pH 2–4, 80 °C) through potentiodynamic/potentiostatic polarization, electrochemical impedance spectroscopy (EIS) and interfacial contact resistance (ICR) measurements. Coatings were characterized via SEM-EDS, TEM and XPS, with particular focus on pH-dependent degradation behavior at both conventional (0.67V) and startup (1.43V) operating potentials. Findings The C/Ti/SS composite coatings significantly reduced the ICR from 312.38 mΩ·cm2 (bare SS316L) to 1.24 mΩ·cm2. In the simulated PEMFC environment, pitting corrosion was identified as the primary failure mechanism of the C/Ti/SS coating: the intermediate Ti layer transformed into TiO2 and dissolved, while the surface C layer oxidized and peeled off, degrading both corrosion resistance and conductivity. Lower pH levels further diminished these properties, as high H+ concentrations dissolved TiO2, accelerated C layer shedding and increased ICR. Additionally, H+ and F– ions penetrated through defects, causing pitting corrosion within the stainless steel substrate and reducing overall corrosion resistance. Originality/value This work presents a novel C/Ti/SS composite coating fabricated via PBAIP, demonstrating enhanced corrosion resistance and conductivity for PEMFC bipolar plates. The multilayered design effectively reduces ICR and mitigates pH-dependent degradation, offering a scalable solution for durable performance in acidic fuel cell environments.