An investigation into polypyrrole-coated 316L stainless steel as a bipolar plate material for PEM fuel cells

Abstract

Increasing attention is being paid to the use of metallic materials as a replacement for non-porous graphite in bipolar plates (BPs) for polymer exchange membrane (PEM) fuel cells. The ideal BP material should demonstrate high values of electrical conductivity, thermal conductivity, corrosion resistance and compressive strength and low values of gas permeability and density. Although metallic materials demonstrate many of those properties, their corrosion resistance can be inadequate, which in turn can lead to unacceptable values of contact resistivity. In this study, polypyrrole was polymerized onto 316L stainless steel using galvanostatic and cyclic voltammometric methods. A dense coating of polypyrrole could be formed on SS316L using both electrochemical methods. The coatings had different morphologies. For galvanostatic coatings, the particle size increases with increasing applied current. For cyclic voltammometric coatings, the particle size increases with increasing the cycle number. The potentiodynamic tests show that the corrosion current density is decreased by about one order of magnitude and polarization resistance is increased by about one order of magnitude by coating with polypyrrole. Optical microscopy showed that there is less intergranular corrosion after coating with polypyrrole. Therefore, these dense polypyrrole coatings much improved the corrosion resistance of SS316L and the coated materials could possibly be used in polymer exchange membrane fuel cells (PEMFCs) as a bipolar plate material.