Self-passivating carbon film as bipolar plate protective coating in polymer electrolyte membrane fuel cell

• W-doped carbon films exhibit low ICR value ranging from 6.25 to 7.21 mΩ-cm2.
• Electrochemical results show carbon film with metallic W has better corrosion resistance.
• Corrosion resistance during pulse polarization is greatly improved by proper W concentration.
• Metallic W on surface is oxidized after polarization enabling self-passivating ability.
• A proper W concentration is preferred while formation of WC by overdoping should be avoided.

The effects of W doping on the microstructure, ICR, and corrosion resistance of carbon films are systematically investigated. The W-doped carbon film has a compact structure and the surface topography changes slightly with W concentration. W exists in mainly the metallic state when the concentration is small, but amorphous WC is formed in the CW2(A) and CW3(A) samples. The ICR at a typical compaction force of 150 N cm−2 increases marginally in the range of 6.25–7.21 mΩ-cm2 as the W concentration is varied. The carbon films with smaller W concentrations have better corrosion resistance and even the self-passivating ability. During pulse polarization, the bare SS316L shows a very large current density of 150 μA cm−2 due to breakdown of the passive film, but CW1(A) shows a stable and low current density of about 0.6 μA cm−2 due to the good self-passivating ability. The self-passivating ability originates from oxidation of metallic state W in the carbon film and so a proper W concentration can yield the desirable self-passivating effect.