PVD carbon and nitride coatings for application in metallic bipolar plates

Bipolar plates are critical components in proton exchange membrane fuel cell (PEMFC) systems. In these systems, replacing graphite bipolar plates (BPPs) with metallic alternatives such as stainless steel (SS) offers advantages in terms of lower density, higher mechanical strength, and improved cost-effectiveness. However, ensuring adequate protection of these metals against corrosion and passivation in the acidic and humid PEMFC environment is essential. This study aims to compare the characteristics of protective coatings deposited by different physical vapor deposition (PVD) techniques onto stainless steel substrates. Carbon coatings were deposited on AISI 304 and AISI 316L substrates using radiofrequency (RF) sputtering, ion beam sputtering (IBS), and pulsed electron deposition (PED), while nitride coatings were produced by RF sputtering. To enhance coating adhesion, various interlayers - including Cr, Si, Ti, Al, and W - were investigated. The coatings were characterized in terms of surface morphology using scanning electron microscopy (SEM) and stylus profilometer. Interfacial contact resistance (ICR) was measured using a dedicated setup under pressures of up to 104.20 N·cm⁻² (measurement configuration shown in Figure 1). Comparative results (Figure 2) indicated that C_PED samples (carbon coatings deposited by PED) exhibited lower ICR values than CrN/Cr samples (chromium nitride coatings deposited by RF sputtering), suggesting superior electrical performance for the PED-derived carbon coatings under the tested conditions.