Thermally nitrided stainless steels for polymer electrolyte membrane fuel cell bipolar plates. Part 2: Beneficial modification of passive layer on AISI446

Thermal nitridation of AISI446 mod-1 superferritic stainless steel for 24 h at 1100 C resulted in an adherent, inward growing surface layer based on (Cr, Fe){sub 2}N{sub 1-x} (x = 0--0.5). The layer was not continuous, and although it resulted in low interfacial contact resistance (ICR) and good cor...

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Bibliographic Details
Published in:Journal of power sources 2004-11, Vol.138 (1-2), p.79-85
Main Authors: WANG, H, BRADY, M. P, MORE, K. L, MEYER, H. M, TURNER, John A
Format: Article
Language:English
Subjects:
30 DIRECT ENERGY CONVERSION
Applied sciences
CORROSION RESISTANCE
Direct energy conversion and energy accumulation
Electrical engineering. Electrical power engineering
Electrical power engineering
Electrochemical conversion: primary and secondary batteries, fuel cells
ELECTROLYTES
Energy
Energy. Thermal use of fuels
Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc
Exact sciences and technology
FERRITES
FUEL CELLS
ION CYCLOTRON-RESONANCE
LAYERS
MATERIALS SCIENCE
MEMBRANES
MODIFICATIONS
NITRIDATION
NITRIDES
NITROGEN
OXIDES
POLARIZATION
POLYMERS
PROTON EXCHANGE MEMBRANE FUEL CELLS
STAINLESS STEELS
SURFACES
TEMPERATURE RANGE 1000-4000 K
UPTAKE
X-RAY PHOTOELECTRON SPECTROSCOPY
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Summary:Thermal nitridation of AISI446 mod-1 superferritic stainless steel for 24 h at 1100 C resulted in an adherent, inward growing surface layer based on (Cr, Fe){sub 2}N{sub 1-x} (x = 0--0.5). The layer was not continuous, and although it resulted in low interfacial contact resistance (ICR) and good corrosion resistance under simulated polymer electrolyte membrane fuel cell (PEMFC) cathodic conditions; poor corrosion resistance was observed under simulated anodic conditions. Nitridation for 2 h at 1100 C resulted in little nitrogen uptake and a tinted surface. Analysis by SEM, XPS, and AES suggested a complex heterogeneous modification of the native passive oxide film by nitrogen rather than the desired microns-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. Further, little increase in ICR was observed under passivating polarization conditions. The potential of this phenomenon for PEMFC bipolar plates is discussed.
ISSN:0378-7753
1873-2755
DOI:10.1016/j.jpowsour.2004.06.064