(702g) Electrically Conductive and Super-Hydrophilic Bipolar Plate Coatings Prepared From Mixed Aqueous Suspensions of Graphene Sheets and Silica Nanospheres

Interfacial chemical domain size and distribution can have a significant influence on the electronic properties of composite coatings. In this paper, we demonstrate how the theoretical predictions of the Gouy-Chapman model for electrostatic interactions between nanoparticles may be used to control heterogeneous chemical domain size and distribution at interfaces. Specifically, we demonstrate through high resolution SEM, TEM, and AFM imaging how the ionic strength, dielectric constant, and pH of suspending media may be systematically altered to vary the three-dimensional distribution of hydrophobic graphene sheets (in the form of ~5 nm thick graphite platelets) and hydrophilic silica nanospheres (~60 nm diameter) simultaneously and irreversibly deposited onto metallic surfaces from mixed suspension utilizing a polymeric binder. The process is used to alter the water wetting properties of bipolar plate materials employed in proton exchange membrane (PEM) fuel cells while maintaining low electrical contact resistance. Such composite coatings are shown to yield advancing contact angles of not more than 10 degrees while maintaining an electrical contact resistance below 5 mΩ-cm² for ~100 nm adsorbed layer thickness. This result represents an order of magnitude reduction in contact resistance relative to that of pure silica coatings of comparable thickness prepared utilizing chemical vapor deposition.