**2.6. Titanium and their coating**

Titanium[33] has been investigated as a suitable material for bipolar plates because of its properties such as low density, good mechanical strength, and high corrosion resistance. Titanium can form an insulating oxide film such as stainless steel. This surface passive film formed significantly increases ohmic losses with the stack resulting in lower power output compared to uncoated 316 SS. To tackle these challenges, further studies on titanium alloys with niobium and tantalum as viable bipolar plate materials showed that the resistivity of their surface oxides were lower than that of pure Ti. It was also found out that INEOS CHLOR patent PEMcoatTM coated on titanium offered an interfacial contact resistance similar to graphite.
