Investigation of C/Al–Cr–N multilayer coatings for stainless steel bipolar plate in polymer electrolyte membrane fuel cells

To improve the corrosion resistance and surface conductivity of stainless steel bipolar plate, C/Al–Cr–N multilayer coatings with varying Al:Cr target current are deposited on stainless steel 316 L (SS316L) by magnetron sputtering. Scanning electron microscope (SEM) results show that the coating is about 2.3 μm in total thickness, consisting of 0.9 μm carbon layer and 1.4 μm Al–Cr–N sub-layer. The interfacial contact resistance (ICR) result indicates that the surface resistance decreases with the increasing content of chromium, and achieves the minimum value of 6.17–4.88 mΩ-cm2 at the compaction force between 120 and 150 N cm− 2 for the Al2Cr4 sample. The electrochemical and inductively coupled plasma atomic emission spectrometry (ICP-AES) results disclose that C/Al–Cr–N multilayer coatings with Cr:N atomic ratio of 1:1 and lower aluminum content have higher chemical inertness and better corrosion resistance. Al6Cr0 and Al5Cr1 samples exhibit more negative corrosion potential and higher passive current density with galvanic corrosion on the surface due to the existence of AlN phase. Therefore, C/Al–Cr–N multilayer coatings with lower aluminum content are preferred for bipolar plate application.