Performance evaluation of TiN/Ti coatings on the aluminum alloy bipolar plates for PEM fuel cells

In this study, different coatings were applied to the bipolar plates (BPs) of proton-exchange membrane fuel cells (PEMFCs). The studied BPs materials include graphite, uncoated Al6061, Al6061 coated with single TiN (0.5 μm) layer, and different composite TiN/Ti layers. Experimental results show that the BP with TiN coating has a higher corrosion potential than those with TiN/Ti coatings, which implies TiN/Ti may have shorter operating life than TiN. The Al6061 with TiN (0.5 μm) has the lowest water contact angle among all the materials. As the Ti proportion on TiN increases, the water contact angle becomes greater, leading to better water removal ability and better fuel cell performance stability. The PEMFC performance with the Al6061 BPs coated with TiN/Ti (0.5μm/0.125 μm) is slightly better than that only coated with TiN. The appropriate thickness of Ti coating improves the PEMFC performance. The BPs made of uncoated Al6061 show the worst performance. After 480-h testing, the cell with uncoated Al6061 BPs has a significant performance degradation due to the increase of the ohmic resistance. The performance degradation rates with TiN/Ti and TiN coated BPs are slightly different, but both coatings significantly improve of the PEMFC life with Al6061 BPs.