| High cost and short lifetime are the two main reasons why the PEM fuel cell has not reached a widespread, disruptive level of commercialization. Conventional graphite bipolar plates are responsible for about 45% of the cost and 85% of the total weight of a single cell. These measures are linked to difficult machining of thick, brittle graphite and processing needed to render graphite non-porous. Stainless steel is suggested as the replacement bipolar plate material due to its favorable mechanical properties, ease of manufacturing and relatively low price, but requires a cost-effective coating as a non-conductive oxide forms on the bare stainless-steel surface in PEMFC environment. This study aims to demonstrate improvements made to PVD coatings of TiN by integrating an additional thin, pure-Ti layer between substrate and coating, as has been extensively studied in integrated circuit manufacturing, biomedical coatings, and thin film photovoltaic applications, to minimize coating defects that currently prevent these coatings from widespread commercial use. We are not aware of any previous studies that have directly evaluated the strategy's effectiveness for stainless steel BPP corrosion protection in PEMFC.;Corrosion tests were performed in H2SO4 electrolyte (pH 3, 70°C) to mimic PEMFC operating condition. Before and after each corrosion test, XPS, ICR, SEM, and ICP-MS techniques were utilized to evaluate coating performance as a corrosion-inhibitor. Results obtained show a multilayer approach with the additional Ti layer improved corrosion resistance as observed through lower ICR, contamination in the TiN film, metal ion poisoning of electrolyte and density/size of cracks and pits in the films. TiN showed significant surface oxide formation which explains the gain in contact resistance to levels above the DOE standard for bipolar plates. |
