Graphene/polyaniline waterborne composite coatings for metallic bipolar plates

Waterborne composite coatings were formulated for protection of metallic bipolar plates. The challenges lied in two aspects, one was the confliction between high electrical conductivity and good corrosion protection properties; the other was the water dispersibility of the constituent phases. Water-solubility of polyaniline (PANI) were controlled by adding polystyrene sulfonic acid during the polymerization of aniline. Graphene was functionalized by p-aminobenzoic acid and p-phenylenediamine to enhance the compatibility with PANI, while keeping the electrical conductivity of graphene at around 169 S/cm. Upon in-situ polymerization of the functionalized graphene/PANI composites, the electrical conductivity varied significantly from 41 S/cm to 91 S/cm with the surface functionality of graphene. The composite coatings were prepared thereafter with functionalized graphene/PANI/carbon black on the surface of 316 L stainless steel by centrifugal spraying coating. The interfacial contact resistance of the coatings reached 4 mΩ·cm², comparable to Au coatings, but the corrosion current density was 4.37 μA/cm² due to the existence of the hydrophilic groups in waterborne coatings, like amino groups and sulfonic acid groups. A post-treatment was carried out to consume some of the amino groups, so that the corrosion current density was decreased to 0.88 μA/cm².