Corrosion resistance and conductivity of amorphous carbon coated SS316L and TA2 bipolar plates in proton-exchange membrane fuel cells

Abstract

Metal bipolar plates (BPs) typically corrode and form a high-resistivity passivation film in the environment of proton-exchange membrane fuel cells (PEMFCs). Surface modification is urgently needed to improve the corrosion resistance and surface conductivity of metal BPs, and their performance is typically closely related to the substrate type and coating characteristics. In this work, the commonly used metal BP substrates SS316L and Grade 2 Titanium (TA2) were selected, and an amorphous carbon (α-C) film was prepared using DC balanced magnetron sputtering. The passivation film defect density and corrosion resistance of SS316L and TA2 were analyzed by electrochemical and Mott–Schottky tests. The influence of the type of substrate on the microscopic morphology and phase composition of the α-C film was systematically studied, and the corrosion resistance, high-potential (1.4 V (SCE)) corrosion, and surface contact resistance of the film were also analyzed. It was found that the film has excellent corrosion resistance at 0.6 V. However, at 1.4 V (SCE), the film on SS316L showed severe local corrosion, while the TA2 sample did not show any local corrosion. This demonstrates that the corrosion resistance of the BPs is dominated by the film at 0.6 V; while at high corrosion potentials, the corrosion resistance of the substrate plays a decisive role.