Surface modification of 304 stainless steels to improve corrosion behavior and interfacial contact resistance of bipolar plates

In this study, plasma nitrided stainless steel (SS304) at low and high temperature, treated by Thermo Reactive Deposition (TRD) and then pickled is investigated under PEMFC accelerated condition. Surface characterization is performed by SEM, EDS, XRD, AFM, and GD-OES. Potentiostatic (PS) and electrochemical impedance spectroscopy (EIS) is used to assess corrosion resistance of untreated and treated samples. Interfacial contact resistance (ICR) measurements are carried out to investigate the surface conductivity. The results reveal that TRD treated samples are covered by an inhomogeneous layer that cannot protect the substrate. Corrosion resistance and conductivity of pickled samples improve significantly. The improvements are attributed to a rich chromium layer and the low roughness of the modified passive layer. A bi-layer (outer porous and inner dense layer) structure is proposed as the most appropriate model for the passive film. Contact angle measurements indicate improved hydrophobicity of pickled samples. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.