SnO 2:F coated austenite stainless steels for PEM fuel cell bipolar plates

Abstract

Austenite stainless steels (316L, 317L, and 349™) have been coated with 0.6 μm thick SnO 2:F by low-pressure chemical vapor deposition and investigated in simulated polymer electrolyte membrane fuel cell (PEMFC) environments. The results showed that substrate steel has a significant influence on the behavior of the coating. Coated 316L showed a steadily increasing anodic current in PEMFC environments, indicating that it is not suitable for this alloy/coating combination. Coated 349™ showed a cathodic current in the PEMFC anode environment, demonstrating its stability in the PEMFC cathode environment. Coated 317L exhibited a stable anodic current after a current peak (at ca. 14 min) in the PEMFC anode environment, and showed an extremely stable low current in PEMFC cathode environment, suggesting the possibility of using SnO 2:F coated 317L for PEMFC bipolar plate applications. ICP results on the corrosion solutions showed that the PEMFC anode environment is much more corrosive than the cathode one. Fresh 316L showed the highest Fe, Cr, and Ni dissolution rates, and coating with SnO 2:F significantly reduced the dissolution. Coating the 317L also showed a significant beneficial effect on the corrosion resistance in the PEMFC environments. Coating 349™ steel further improved the already excellent corrosion resistance of this alloy. Trace Sn ions were detected for all coated steels in PEMFC anode environment, but not in the cathode one. The influence of SnO 2:F on the interfacial contact resistance (ICR) is mixed. For 316L and 317L steels, a SnO 2:F coating reduced the ICR. For 349™ steel, the SnO 2:F coating increased the ICR.