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Research Papers

# Plasma Nitrided Type 349 Stainless Steel for Polymer Electrolyte Membrane Fuel Cell Bipolar Plate—Part II: Nitrided in Ammonia 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), 021019 (Jan 19, 2010) (6 pages) doi:10.1115/1.3178640 History: Received April 28, 2008; Revised April 10, 2009; Published January 19, 2010; Online January 19, 2010

## Abstract

Austenitic 349 stainless steel was nitrided in an $NH3$ plasma. A low interfacial contact resistance was obtained with the nitrided steel. Glancing angle X-ray diffraction suggests that the nitrided layer is very thin and possibly amorphous. X-ray photoelectron spectroscopy (XPS) studies show that the nitrided layer is composed of mixed oxides and nitrides of $Fe3+$ and $Cr3+$. Contaminations of V and Sn were also observed, though their influence on the as-nitrided surface conductivity is not clear. The nitrided samples were investigated in a simulated polymer electrolyte membrane fuel cell (PEMFC) environment, and showed excellent corrosion resistance. The XPS depth profile indicated that the passive film, which formed on the plasma-nitrided steel in the PEMFC anode environment, is composed of mixed oxides and nitrides, in which chromium oxide/nitride dominates the surface chemistry. No V or Sn was detected on the surface after the polarization tests. For the PEMFC bipolar plate application, nitridation in $NH3$ plasma is a promising surface treatment approach, though more research is needed to investigate the influence of the plasma density and substrate bias on the surface conductivity and performance of the nitrided steel in PEMFC environments.

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## Figures

Figure 1

Anodic polarization curves for bare and plasma-nitrided 349 SS in 1 M H2SO4+2 ppmF− solution at 70°C purged with (a) air and (b) hydrogen gas. The scanning rate was 1 mV/s and the scan was from OCP to anodic.

Figure 2

Transient currents for nitrided 349 SS in NH3 plasma (a) at 0.6 V when the solution was purged with air in a simulated PEMFC cathode environment, and (b) at −0.1 V when the solution was purged with hydrogen gas in a simulated PEMFC anode environment. Inset of (b) shows the accumulated charge during the first hour of polarization.

Figure 3

Influence of nitriding in NH3 plasma and polarization on the interfacial contact resistance of 349 SS/carbon paper interface

Figure 4

Glancing angle X-ray diffraction pattern obtained for 1 h nitrided 349 SS in NH3 plasma

Figure 5

XPS spectra obtained from 1 h nitrided 349 SS sample in NH3 plasma: (a) Fe2p, (b) Cr2p, (c) O1s, and (d) N1s photoelectron peaks

Figure 6

XPS depth profiles for 1 h nitrided 349 SS in NH3 plasma. Inset shows the surface nitrogen and bulk nitride distributions.

Figure 7

XPS depth profiles for 1h NH3 plasma-nitrided 349 SS polarized at −0.1 V for 7.5 h in a simulated PEMFC anode environment. Inset shows the surface NH3 and bulk nitride concentrations.

Figure 8

Influence of nitriding in NH3 plasma and polarization in simulated PEMFC environments on the total nitrogen concentration of 349 SS

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