Investigation of hydrophobic and anti-corrosive behavior of Cr-DLC film on stainless steel bipolar plate

Abstract

In order to improve the corrosion resistance and hydrophobic electrical resistivity of stainless steel bipolar plate (BPP) of polymer electrolyte membrane fuel cell (PEMFC), diamond-like carbon doped with Cr (Cr-DLC) films with different Cr content were fabricated on stainless steel 304 without transition layer via magnetron sputter. The surface morphology, structure, hydrophobic properties, electrical resistivity, and corrosion resistance of the samples were analyzed. As the power of the graphite target increased, the sp2C content and surface roughness of the films first decreased and then increased. The results showed that all the films increased the contact angle and improved the corrosion resistance of the substrates. Especially, the sample with Cr content of 2.58 at.% showed a relatively higher contact angle and better corrosion resistance in different solutions. It showed the lowest current density of 6.5 × 10−8 A/cm2 and 2.59 × 10−8 A/cm2 in 3.5 % NaCl solution and 0.1 M H2SO4 solution, respectively. Additionally, the corrosion potential of it was −0.5 mV in 0.1 M H2SO4 solution, which was much higher than the substrate. The excellent corrosion resistance of the sample with a Cr content of 2.58 at.% was attributed to the lower surface roughness, passivation of the Cr2O3 on its surface, and the inertness of CrxCy, which compensated for pinhole defects during the corrosion tests. The results convinced that Cr-DLC film exhibits excellent properties that can supply an option for stainless steel used as BPP.