C. K. Chandra¹, M. Salvador², R. Reitz¹, H. Hoche¹, P. Kaestner², G. Bräuer², M. Oechsner^1
1TU Darmstadt, Darmstadt, Germany
²TU Braunschweig, Braunschweig, Germany
Metallic bipolar plates for PEM-fuel cells (FC) must combine low interfacial contact resistance (ICR) with long-term corrosion resistance in aggressive, fluoride-containing environments. While the passive chromium-oxide film on austenitic steel 1.4404 (AISI 316L) provides excellent corrosion protection, it significantly increases ICR. Low-temperature plasma nitriding (LT-PN) has been shown to form expanded austenite, reducing the ICR by a factor of approx. 100x compared to untreated state. However, massive reduction in corrosion resistance appears to accompany this improvement. Low-temperature plasma carburizing (LT-PC), which is expected to create a carbon-enriched, graphite-like expanded austenite, could offer significantly higher electrical conductivity in comparison to LT-PN.
A comprehensive test program is employed to benchmark LT-PC against LT-PN. Potentiodynamic and potentiostatic polarization combined with electrochemical impedance spectroscopy are carried out under simulated PEM-FC operating conditions to assess the corrosion behavior. The ICR is measured under controlled mechanical compression before and after the corrosion tests. Supporting surface and microstructural analyses were employed to identify the degradation mechanisms.
This work highlights electrochemical testing and surface characterization of AISI 316L treated with LT-PN and LT-PC. The results provide fundamental insights into the underlying mechanisms that govern corrosion resistance and ICR, paving the way for next-generation bipolar plates in PEM-FC applications.