Cerium insertion in 316L passive film: Effect on conductivity and corrosion resistance performances of metallic bipolar plates for PEM fuel cell application

A surface treatment to modify passive film properties formed on 316L stainless steel has been designed for bipolar plate application in PEMFC systems. This one is based on cerium insertion from electrochemical technique. The effect of this element addition on the composition of the passive films was evaluated by X-ray photoelectron spectroscopy (XPS) and low energy ion spectroscopy (LEIS). Potentiodynamic and potentiostatic curves, and electrochemical impedance spectroscopy (EIS) were used for the characterisation of the corrosion protection in simulated PEMFC media. Interfacial contact resistance (ICR) was also evaluated. Results highlight an increase of the polarisation resistance of the cerium treated sample at ambient temperature, and a good corrosion resistance in anodic and cathodic simulated media. An important diminution of the IRC is obtained (80% with respect to the reference), which is attributed to the enhancement of the passive layer conductivity of the processed sample. Surface analyses show a great enrichment of cerium in first atomic layers of the films, which explains the better conductivity observed by an increase of charge carrier density in the passive film.