Interface-induced degradation of amorphous carbon films/stainless steel bipolar plates in proton exchange membrane fuel cells

Abstract

In the field of proton exchange membrane fuel cells (PEMFCs), amorphous carbon (a-C) films have attracted considerable attention as a surface functional coating for metallic bipolar plates (BPPs), given that they can endow metallic BPPs with both high corrosion resistance and electrical conductivity under harsh PEMFC environments. In this study, to determine the role of a-C/metallic substrate interfaces on the performance of PEMFCs, and clarify the associated degradation mechanism, a series of a-C films are deposited on 316L stainless steel (316Lss) samples at different sputtering powers. The composition, microstructure, interfacial contact resistance (ICR), and corrosion resistance of the a-C films are then systemically investigated, before and after electrochemical corrosion tests. The results obtained reveal that all the a-C films can greatly improve the performance of 316Lss under simulated PEMFC operational conditions, and the a-C film deposited at 0.9 kW exhibits the lowest corrosion current density (~7.52 × 10−3 μA cm−2) and minimum ICR values (2.91 and 4.00 mΩ cm2, before and after the long-time potentiostatic polarization tests, respectively). Furthermore, residual chromium oxides, which possibly result in an increased in ICR values, are observed at the a-C/316Lss interface after corrosion test; thus, an interface-induced a-C film degradation mechanism is proposed.