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Nerima-ku, Japan

Kumagai M.,Japan National Institute of Materials Science | Kumagai M.,Taiyo Stainless Spring Co. | Myung S.-T.,Sejong University | Yashiro H.,Iwate University | Katada Y.,Japan National Institute of Materials Science
Journal of Power Sources | Year: 2012

The purpose of this report is to directly observe the passive layer and concentration behavior of nitrogen interstitially incorporated in Ni-saving high nitrogen stainless steel (HNS) using an aberration corrected scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) or - electron energy loss spectroscopy (EELS). The thickness of the passive layer barely changed after 1000 h single cell operation, compared with the as-polished state. The observed passive layer was thin (3 nm) and mainly composed of chromium oxide, as confirmed by STEM-EDS. It was confirmed that nitrogen was not present in the passive layer, but was concentrated at the interface between the passive layer and the metal bulk. The concentrated area ranged approximately 2 nm to steel bulk from the interface. With help of the STEM-EDS and EELS, we were able to understand the nature of the passive layer for Ni-saving HNS, which caused remarkable improvement of the cell performance due to superior corrosion resistance. © 2012 Elsevier B.V. All rights reserved. Source

Kumagai M.,Japan National Institute of Materials Science | Kumagai M.,Taiyo Stainless Spring Co. | Myung S.-T.,Sejong University | Ichikawa T.,Iwate University | And 2 more authors.
Journal of Power Sources | Year: 2012

In the present paper, we elucidate the possible reasons for high voltage retention during operation when a Ni-saving high nitrogen stainless steel (hereafter referred as to Ni-saving HNS) was used as bipolar plates for PEMFCs. A typical type 316L was also employed as bipolar plates to compare the cell performance. The Ni-saving HNS bipolar plate adopting cell obviously exhibited better cell performance at various current densities. After 1000 h of cell operation, the tested metallic bipolar plates were analyzed by scanning electron microscopy, inductively coupled plasma-mass spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy-energy-dispersive X-ray spectroscopy, and transmission electron microscopy-electron energy loss spectroscopy to prove the superiority of the Ni-saving HNS bipolar plates. As a result, the surface state of the bipolar plates exposed to the PEMFCs environment is the critical factor that affects cell performance. Protection of the metal surface mainly with chromium oxide-based surface layer, which was induced from a reaction of N from the Ni-saving HNS and H 2O generating proton, H +, that lowers local surface pH, was thus substantially effective to retain the voltage upon operation. © 2011 Elsevier B.V. All rights reserved. Source

Yashiro H.,Iwate University | Yokosawa Y.,Iwate University | Kure S.,Iwate University | Chu S.,Iwate University | And 3 more authors.
Zairyo to Kankyo/ Corrosion Engineering | Year: 2013

Type 310S stainless steel cathodically treated in a nitric acid - nitrate solution in anticipation of formation of conductive nitrides has been evaluated in terms of contact resistance against gas dif fusion layer(GDL), polarization behavior, surface chemical state and PEFC performance when used as bipolar plate. The contact resistance between the treated stainless steel and GDL did decrease to the demanded level. XPS analysis indicated formation of thin nitride layer on stainless steel among oxides. The thickness of the nitride layer was within a few nanometers but was stable even after anodic polarization at 0.6 V vs. SCE. The cathodic treatment was applied to stainless steel bipolar plates for operation of a single cell. The cell performance was comparable to that with graphite bipolar plates, suggesting great promise as a convenient surface treatment for stainless steel bipolar plates. Source

Kumagai M.,Taiyo Stainless Spring Co. | Myung S.-T.,Iwate University | Ichikawa T.,Iwate University | Yashiro H.,Iwate University
Journal of Power Sources | Year: 2010

Ferritic stainless steels can be attractive bipolar plate materials of proton exchange membrane fuel cells (PEMFC), provided that the stainless steels show sufficient corrosion resistance, for instance, by eliminating interstitial elements such as carbon and nitrogen. In the present study, thus, ferritic stainless steels (19Cr2Mo and 22Cr2Mo) with extra low interstitials (ELI) are evaluated to determine the required level of chromium content to apply them for PEMFC bipolar plates. In a simulated PEMFC environment (0.05 M SO 4 2- (pH 3.3) + 2 ppm F- solution at 353 K), the 22Cr2Mo stainless steel showed lower current density during the polarization in comparison with the 19Cr2Mo one. The polarization behavior of the 22Cr2Mo stainless steel resembles that of the type 316 one (17Cr12Ni2Mo). Similar values of interfacial contact resistance (ICR) are observed for both ferritic stainless steels. The 22Cr2Mo stainless steel bipolar plate is found to be stable throughout the cell operation, while the 19Cr2Mo stainless steel corroded within 1000 h. After the cell operation, the 22Cr2Mo stainless steel retains the chromium enriched passive film, while the chromium enriched surface film is not found for the 19Cr2Mo one, showing iron oxide/hydroxide based film. X-ray fluorescence (XRF) analysis of the membrane electrode assemblies (MEAs) after the cell operation indicates that the 22Cr2Mo stainless steel was less contaminated with iron species. The above results suggest that the 22Cr2Mo stainless steel can be applicable to bipolar plates for PEMFC, especially 22 mass% of chromium content in ferritic stainless steel with ELI system is, at least, demanded to ensure stable cell performance. © 2010 Elsevier B.V. Source

Myung S.-T.,Iwate University | Sakurada S.,Iwate University | Kumagai M.,Taiyo Stainless Spring Co. | Yashiro H.,Iwate University
Fuel Cells | Year: 2010

In order to utilise inexpensive bipolar plates for proton exchange membrane fuel cells (PEMFC), a surface modification with TiN nanoparticles and elastic styrene butadiene rubber (SBR) particles has been applied to the most widely commercialised stainless steel of type 304 which did not satisfy the required properties in the bare form. The electroconducting agglomerates were electrophoretically deposited on the stainless steel bipolar plates. The surface modification greatly improved the corrosion resistance of the stainless steel as well as the interfacial contact resistance (ICR). As a result, the cell performance was significantly enhanced and become comparable to that with graphite bipolar plate during operation for 1,000 h. Ac-impedance results indicated that the TiN-SBR coating was effective not only in reducing the ICR but also in retaining the resistance low throughout the operation. The hydrophobic character of the TiN-SBR coating on the stainless steel bipolar plates, which facilitated the removal of the formed water in the cathode side during the single cell operation, is also responsible for the enhanced cell performance. Therefore, the type 304 stainless steel bipolar plate modified with the electro-conducting nanosized TiN - elastic SBR particles is suggested to be a promising substituent for the PEMFC graphite bipolar plate. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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