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Research Papers

Plasma Nitrided Type 349 Stainless Steel for Polymer Electrolyte Membrane Fuel Cell Bipolar Plate—Part I: Nitrided in Nitrogen Plasma

[+] Author and Article Information
Heli Wang1

 National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401heli.wang@nrel.gov

Glenn Teeter, John A. Turner

 National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401

1

Corresponding author.

J. Fuel Cell Sci. Technol 7(2), 021018 (Jan 19, 2010) (7 pages) doi:10.1115/1.3178555 History: Received April 28, 2008; Revised April 10, 2009; Published January 19, 2010; Online January 19, 2010

An austenite 349 stainless steel was nitrided via nitrogen plasma. Glancing angle X-ray diffraction patterns suggest that the nitrided layer is amorphous. X-ray photoelectron spectroscopy analysis indicated that the plasma nitridation process produced bulk-type nitrides in the surface layer. In general, the nitrided layer was composed of iron oxide in the outer layer and chromium oxide in the inner layers. Contaminations of vanadium and tin were detected in the as-grown nitrided layer; these dissolved away after polarization. The influence of these contaminants on the corrosion resistance of the nitrided layer in polymer electrolyte membrane fuel cell (PEMFC) environments is not considered significant. The nitrided sample had a much higher contact resistance than the bare one and the contact resistance increased with the nitriding time. The high interfacial contact resistance values can be related to the thicker oxide film after plasma nitridation. The corrosion resistances obtained for the 1 h nitrided and bare stainless steels in simulated PEMFC environments were similar. The outmost nitrided layer dissolved after polarization in the PEMFC environments leaving a passive film (modified with nitrides), similar to that of bare stainless steel under the same conditions. The passive film thickness was 3.7 nm for nitrided steel in PEMFC cathode environment and 4.2 nm for nitrided steel in PEMFC anode environment.

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References

Figures

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Figure 1

Influence of plasma nitriding on the anodic behavior of 349 SS in 1 M H2SO4+2 ppmF− at 70°C purged with air (a) or hydrogen gas (b). Scanning rate was 1 mV/s.

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Figure 2

Influence of plasma nitriding on the potentiostatic behavior of 349 SS in 1 M H2SO4+2 ppmF− at 0.6 V when the solution was purged with air (a) and at −0.1 VSCE when the solution was purged with hydrogen gas (b)

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Figure 3

(a) Influence of plasma nitriding on the interfacial contact resistance between 349 SS and conductive carbon paper and (b) influence of 7.5 h polarization in PEMFC cathode environment (0.6 V, air purge) on the interfacial contact resistance for plasma-nitrided 349 SS and bare steels

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Figure 4

Glancing angle XRD patterns obtained for bare 349 SS (a) and for 3 h plasma-nitrided 349 SS treated in nitrogen plasma (b)

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Figure 5

XPS depth profile of air-formed oxide film on bare 349 SS surface. Inset shows surface nitrogen and bulk nitrides distribution.

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Figure 6

XPS depth profiles obtained for 349 SS nitrided 1 h in nitrogen plasma. Inset shows surface nitrogen and bulk nitrides distributions.

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Figure 7

XPS depth profile obtained after 7.5 h polarization in simulated PEMFC cathode environment for 1 h plasma-nitrided 349 SS treated in nitrogen plasma. Inset shows surface nitrogen and bulk nitrides distributions.

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