Ultrathin effective TiN protective films prepared by plasma-enhanced atomic layer deposition for high performance metallic bipolar plates of polymer electrolyte membrane fuel cells

Abstract

The stainless steel (SS)-based bipolar plate with high conductivity and corrosion resistance is one of the key components in recent polymer electrolyte membrane fuel cells. Therefore, an excellent corrosion protection and good electrical conductivity in SS316L-based bipolar plates can be achieved through plasma-enhanced atomic layer deposition (PEALD) of ultrathin (25–67 nm) TiN thin films. To this end, two types of TiN protective coatings deposited by PEALD using tetrakis(dimethylamino)titanium (TDMAT) and titanium tetrachloride (TiCl4) precursors were evaluated; the evaluations were conducted under conditions simulating the operating conditions of PEMFCs. Regardless of the precursor type, PEALD-TiN onto SS316L resulted in great improvements in electrical conductivity and corrosion resistance. Notably, the TiN thin films prepared using TDMAT exhibited excellent corrosion resistance (<1 μA/cm2) compared to those produced using TiCl4 as the precursor. Systematically structural, compositional, and electrochemical analysis revealed that a ~5-nm-thick ultrathin amorphous interfacial layer, formed and played a key role in the corrosion protection using TDMAT. Furthermore, the TiN thin films by TDMAT greatly lowered the interfacial contact resistance of SS316L from 35.868 to 15.239 mΩ∙cm2 at a compaction force of 127 N/cm2. Our study presents an interesting opportunity for the development of PEALD protective coating materials for SS-bipolar plates.