Rajib Paul, Michael Hysick, Isabelle Leonard, Robert Stubbers, Brian Jurczyk, Starfire Industries LLC, Champaign, IL
Recently commercialization aspects of proton-exchange-membrane-fuel-cells (PEMFCs) have been researched extensively to reduce the energy costs down to $1/kW. Metal bipolar plates (BPPs) are the most expensive but important components of PEMFC-stacks because they are better than graphite and composite BPPs due to their superior mechanical, electrical and thermal properties. However, metal BPPs need protective coatings with low interfacial contact resistance (ICR < 10 mΩ-cm² at 1.4 MPa) and high corrosion resistance (corrosion current, I_corr <1mA/cm²). Here we report development of precision-engineered layered TiN thin films on stainless steel (SS316L) substrates and BPPs as a long-lasting anticorrosion coating using IMPULSE^® + Positive Kick^TM next-generation high-power impulse magnetron sputtering (HiPIMS) with precision ion energy and thin-film morphology control. The TiN coating with layered microstructural morphology on SS BPP demonstrated interfacial contact resistance of 1.7±0.2 mΩ.cm² which is one of the best results reported so far. The TiN film demonstrated high corrosion resistances in simulated cathode and anode conditions as per DOE requirements and achieved stable corrosion current of 0.32mA/cm² beyond 20,000s which is again one of the best values as per the literature. After corrosion, no mechanical failure of TiN-film was observed except surface oxidation for cathode condition. We have demonstrated recycling prospects of old bipolar plates; etching out TiN film entirely from the SS bipolar plate surface with an etching rate of 0.15nm/sec so that new coating can be applied. The wear/mechanical testing of TiN film before and after corrosion tests were also performed with attractive prospects. This study helps DOE and related industries to attain the shot-goal of $1 per 1 kg hydrogen generation for PEMFC stacks in heavy duty vehicles.

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