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Research Papers

# Factors Affecting the Formation of Carbon Film on the Stainless Steels for the Bipolar Plate of Polymer Electrolyte Fuel Cells

[+] Author and Article Information
Yoshiaki Matsuo, Shin-ich Miyano, Yosohiro Sugie

Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha Himeji, Hyogo, 671-2201, Japan

Tomokazu Fukutsuka

Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto daigaku-Katsura, Nishikyo-ku, Kyoto 615-8530, Japan

J. Fuel Cell Sci. Technol 8(3), 031008 (Feb 22, 2011) (5 pages) doi:10.1115/1.4003017 History: Received February 22, 2010; Revised October 28, 2010; Published February 22, 2011; Online February 22, 2011

## Abstract

Factors affecting the formation of carbon film by plasma-assisted chemical vapor deposition on stainless steels were investigated in detail. When the carbon coating time increased, the morphology and crystallinity of the formed carbon changed. The depth profile of the resulting carbon coated sample indicated that it was consisted of top carbon layer without metal species and interfacial layer mainly containing chromium oxide and carbon of lower crystallinity. The top carbon layer with the morphology similar to that of carbon nanowall effectively covered the surface of the metal substrate, providing the high electrochemical stability in an acidic solution. As the cold working rate of the stainless steel substrate increases, the time needed for the complete coverage of the metal surface became shorter. Based on the scanning electron microscopy observation and X-ray diffraction, this was mainly ascribed to the increase in defects where the nucleus formation of carbon can occur and the increased density of carbon on the surface of the metal. The resulting carbon coated stainless steels showed low interfacial resistance and high corrosion resistance in acidic solution even at $80°C$, and is promising for the bipolar plate of polymer electrolyte fuel cells.

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## Figures

Figure 11

Polarization curve of SUS304A sample with 9% of cold working, after carbon coated for 180 min in 0.5 M H2SO4 solution at 80°C under O2 gas bubbling. The dotted lines at 10−3 mA/cm2 are guides for eyes.

Figure 10

Polarization curves of carbon coated SUS304A (a) before and (b) after polishing with water proof abrasive paper of #2000, together with that of (c) SUS304A mirror-polished with alumina powder of 10 μm in 0.5 M H2SO4 solution at room temperature under N2 gas bubbling. The dotted lines at 10−3 mA/cm2 are guides for eyes.

Figure 9

X-ray diffraction patterns of SUS304A (a) before and (b) after polishing with water proof abrasive paper of #2000, together with that of (c) SUS304A mirror-polished with alumina powder of 10 μm. The letters “α’” and “γ” denote the martensite and austenite phases, respectively.

Figure 8

Polarization curves of SUS304B samples with various ratios of cold working of (a) 9%, (b) 30%, (c) 50%, and (d) 76%, after carbon coated for 10 min in 0.5 M H2SO4 solution at room temperature under N2 gas bubbling. The dotted lines at 10−3 mA/cm2 are guides for eyes.

Figure 7

X-ray diffraction patterns of the (a) SUS304A and SUS 304B substrates cold worked at various ratios of (b) 0%, (c) 9%, (d) 30%, (e) 50%, and (f) 76%. The letters “α’” and “γ” denote the martensite and austenite phases, respectively.

Figure 6

SEM image of the SUS 304B substrates cold worked at various ratios of (a) 0%, (b) 9%, (c) 30%, (d) 50%, and (e) 76%, together with that of (f) SUS304A. The white arrows indicate the directions of rolling.

Figure 5

Polarization curves of SUS304A carbon coated for (a) 0 min, (b) 10 min, (c) 30 min, (d) 60 min, and (e) 180 min in 0.5 M H2SO4 solution at room temperature under N2 gas bubbling. The dotted lines at 10−3 mA/cm2 are guides for eyes.

Figure 4

Auger depth profiles of carbon, iron, chromium, nickel, and oxygen atoms in SUS304A carbon coated for 180 min

Figure 3

SEM images of SUS304A (a) before and after carbon coated for (b) 10 min, (c) 30 min, (d) 60 min, and (e) 180 min

Figure 2

Raman spectra of SUS304A carbon coated for (a) 10 min, (b) 30 min, (c) 60 min, and (d) 180 min

Figure 1

Variation in the interfacial contact resistance of carbon coated SUS304A as a function of coating time

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