N+-Implantation on Nb Coating as Protective Layer for Metal Bipolar Plate in PEMFCs and Their Electrochemical Characteristics

Abstract

Nitrogen ions were implanted into the coated Nb layer by plasma immersion ion implantation to improve resistance to corrosion of a metal bipolar plate. Due to nitrogen implantation, the corrosion behavior of the Nb layer was enhanced. The electron microscope observation reveals that the microstructure of the Nb layer became denser and had fewer defects with increasing implantation energy. As a result, the densified structure effectively prevented direct contact with the corrosive electrolyte. In addition, at a higher implantation rate (6.40 × 1017 N2/cm2), a thin amorphous layer was formed on the surface, and the implanted nitrogen ions reacted at neighboring Nb sites, resulting in the localized formation of nitrides. Such phase and structural changes contributed to further improve corrosion resistance. In particular, the implanted Nb layer at bias voltage of 10 kV exhibited a current density more than one order of magnitude smaller with a two times faster stabilization than the as-deposited Nb layer under the PEMFC operating conditions.

Surface Engineering & Coating Technologies for Corrosion and Tribocorrosion Resistance

“…Surface engineering and coating technologies have been used to protect the surface of bipolar plates. In the work reported in [ 11 ], Kim et al deposited a Nb coating on stainless steel, followed by N + ion implantation. The authors studied the composition, structure and corrosion performance of the duplex-treated material and found that N+ implantation effectively modified the deposited Nb coating to form an improved protective film with much enhanced corrosion resistance for the metal bipolar plate.…”

“…The authors studied the composition, structure and corrosion performance of the duplex-treated material and found that N+ implantation effectively modified the deposited Nb coating to form an improved protective film with much enhanced corrosion resistance for the metal bipolar plate. This work provides new possibilities for surface modification to improve fuel cell performance and for other applications [ 11 ].…”