Investigation of graphite conductive adhesive coated on SS316L used for bipolar plates of proton-exchange membrane fuel cell

Abstract

The metallic bipolar plates (BPs) in the Proton-Exchange Membrane Fuel Cells (PEMFCs) are usually made of a coating of TiN on Stainless Steel 316 L (SS316L) by the sputtering method. However, the adhesion of ceramic layers such as TiN to SS316L by physical vapor deposition methods is weak, and the coating process is expensive. In this research, the polymer-based carbon adhesive is used as a conductive coating on the SS316L BP. The adhesives are made of polyvinyl acetate cellulose (PVAc) as binder and 40, 50, 60, and 70 wt.% graphite (G) as filler. The strength, density, pore content, electrical conductivity of carbon adhesive, electrochemical corrosion resistance, and Interfacial Contact Resistance (ICR) between carbon-coated BP with Gas Diffusion Layer (GDL) are investigated and are compared with TiN coatings. It was specified that G in the adhesive matrix preserves the crystalline structure and conductivity. However, the carbon coating by other methods such as CVD and PVD creates an amorphous structure containing a high-defect disordered graphitic structure that dramatically influences the ICR value. The lower corrosion current density was obtained for the PVAc films reinforced by 40 and 50 wt.% G (5.41 and 5.90 µA/cm2, respectively), which is about seven order of magnitude less than the substrate (35.10 µA/cm2). Overall, the adhesive of PVAc/60 wt.% G is suggested as a proper coating for SS316L used for BP.