Mass-Producible, Lightweight, and Highly Durable Aluminum Bipolar Plates for PEM Fuel Cells via Magnetron-Sputtered Ta/Ti Bilayer Coatings

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Abstract
In this study, we used a magnetron sputtering process to develop a Tantalum (Ta)/Titanium (Ti) bilayer-coated aluminum (Al) bipolar plate (BP) for polymer electrolyte membrane fuel cells (PEMFCs). To elucidate the effect of the coating thickness on the protective performance, a comparative analysis was performed under various deposition conditions, consisting of (1, 3, and 5) μm Ta single layers and Ta/Ti bilayers of (1 and 4) μm Ti deposited on a 5 μm Ta layer.Electrochemical evaluation results revealed that compared to the Ta single layer, the Ta/Ti bilayer structure exhibited superior protective performance. In particular, the Ta/Ti (5 μm/4 μm) bilayer coating, which exhibited the best performance among the tested conditions, recorded an extremely low current density of 0.175 μA·cm⁻² at 0.86 V vs RHE after 24h under a simulated PEMFC cathode environment. To verify the effectiveness under actual operating conditions, single cell tests were performed. The cell employing the Ta/Ti bilayer-coated Al BP demonstrated excellent performance, achieving a peak power density equivalent to 87 % of that using a commercial graphite BP. Furthermore, during a 24 h durability test, the cell with the Ta/Ti bilayer maintained stable behavior without voltage loss. These results suggest that the Ta/Ti bilayer-coated Al BP developed in this study possesses adequate performance for application in actual PEMFC systems, satisfying the technical target of the U.S. Department of Energy under a simulated PEMFC cathode environment during the 24 h corrosion test.

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