AVS 51st International Symposium
    Applied Surface Science Monday Sessions
       Session AS-MoP

Paper AS-MoP18
Thermally Nitrided Stainless Steels for Polymer Electrolyte Membrane Fuel Cell Bipolar Plates: Beneficial Modification of Passive Layer on AISI446

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: H.M. Meyer III, Oak Ridge National Laboratory
Authors: H.M. Meyer III, Oak Ridge National Laboratory
M.P. Brady, Oak Ridge National Laboratory
K.L. More, Oak Ridge National Laboratory
B. Yang, Oak Ridge National Laboratory
H. Wang, National Renewable Energy Laboratory
J.A. Turner, National Renewable Energy Laboratory
Correspondent: Click to Email
Proton exchange membrane fuel cells (PEMFCs) are of great current interest for power generation due to their high efficiency and environmentally friendly, near-zero emissions. Since cost is critical, metal alloys would be ideal as bipolar plates but suffer from inadequate corrosion behavior due to high electrical resistance by the formation of surface oxides or degrade cell performance by contaminating the membrane with metal ions. Recently, it was discovered that thermally grown Cr nitrides (CrN/Cr2N) on a model Cr-bearing alloy, Ni-50Cr (wt%), show great promise for corrosion resistance and electrical conductivity in PEMFC bipolar plate environments @fototnote 1@. Work is ongoing to form similar nitride surfaces on less expensive Ni-Cr and Fe-Cr base alloys. This poster describes an effort to use a relatively inexpensive ferritic stainless steel (AISI446 MOD-1) as bipolar plate material and specifically looks at its surface chemistry, corrosion resistance, and interfacial contact resistance. Thermal nitridation for 2 h at 1100ºC resulted in little nitrogen uptake and a tinted surface. Analysis by SEM, XPS, and AES suggests a complex heterogeneous modification of the native passive oxide film by nitrogen, rather than the desired micron range thick exclusive Cr-rich nitride layer. Surprisingly, this modification resulted in both good corrosion resistance under simulated cathodic and anodic conditions and low ICR, well over an order of magnitude lower than the untreated alloy@footnote 2@. Details of the nitrided surface chemistry of this alloy will be presented. @FootnoteText@ @footnote 1@ M.P. Brady, K. Weisbrod, I. Paulauskas, R.A. Buchanan, K.L. More, H. Wang, M. Wilson, F. Garzon, L.R. Walker, Scripta Materialia, 50(7) pp.1017-1022 (2004).@footnote 2@ H. Wang, M P. Brady, K.L. More, H.M. Meyer III, and J. A. Turner. Submitted to Journal of Power Sources.