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Journal Articles

Electronic structure of a (3$$times$$3)-ordered silicon layer on Al(111)

Sato, Yusuke*; Fukaya, Yuki; Cameau, M.*; Kundu, A. K.*; Shiga, Daisuke*; Yukawa, Ryu*; Horiba, Koji*; Chen, C.-H.*; Huang, A.*; Jeng, H.-T.*; et al.

Physical Review Materials (Internet), 4(6), p.064005_1 - 064005_6, 2020/06

 Times Cited Count:1 Percentile:32.54(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Magnetic and electronic properties of B-site-ordered double-perovskite oxide La$$_{2}$$CrMnO$$_{6}$$ thin films

Yoshimatsu, Kohei*; Ishimaru, Junya*; Watarai, Keisuke*; Yamamoto, Kohei*; Hirata, Yasuyuki*; Wadachi, Hiroki*; Takeda, Yukiharu; Horiba, Koji*; Kumigashira, Hiroshi*; Sakata, Osami*; et al.

Physical Review B, 99(23), p.235129_1 - 235129_8, 2019/06

 Times Cited Count:4 Percentile:40.4(Materials Science, Multidisciplinary)

Journal Articles

Role of residual transition-metal atoms in oxygen reduction reaction in cobalt phthalocyanine-based carbon cathode catalysts for polymer electrolyte fuel cell

Kobayashi, Masaki*; Niwa, Hideharu*; Harada, Yoshihisa*; Horiba, Koji*; Oshima, Masaharu*; Ofuchi, Hironori*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; et al.

Journal of Power Sources, 196(20), p.8346 - 8351, 2011/10

 Times Cited Count:27 Percentile:30.81(Chemistry, Physical)

The electronic structure of Co atoms in CoPc-based carbon catalysts, which were prepared by pyrolyzing a mixture of CoPc and phenol resin polymer up to 1000$$^circ$$C, has been investigated using XAFS analysis and HXPES. The Co K XAFS spectra show that most of the Co atoms are in the metallic state and small quantities of oxidized Co components are present in the samples even after acid washing to remove Co atoms. Based on the difference in probing depth between XAFS and HXPES, it was found that after acid washing, the surface region with the aggregated Co clusters is primarily composed of metallic Co. Since the electrochemical properties remain almost unchanged even after the acid washing process, the residual metallic and oxidized Co atoms themselves will hardly contribute to the ORR activity of the CoPc-based carbon cathode catalysts, implying that the active sites of the CoPc-based catalysts primarily consist of light elements such as C and N.

Journal Articles

X-ray photoemission spectroscopy analysis of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells

Niwa, Hideharu*; Kobayashi, Masaki*; Horiba, Koji*; Harada, Yoshihisa*; Oshima, Masaharu*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; Miyata, Seizo*; et al.

Journal of Power Sources, 196(3), p.1006 - 1011, 2011/02

 Times Cited Count:77 Percentile:7.25(Chemistry, Physical)

We report on the electronic structure of three different types of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells observed by hard X-ray photoemission spectroscopy. C 1s spectra show the importance of $$sp^{2}$$ carbon network formation for the oxygen reduction reaction (ORR) activity. Samples having high oxygen reduction reaction activity in terms of oxygen reduction potential contain high concentration of graphite-like nitrogen. Based on a quantitative analysis of our results, the oxygen reduction reaction activity of the carbon-based cathode catalysts will be improved by increasing concentration of graphite-like nitrogen in a developed $$sp^{2}$$ carbon network.

Journal Articles

X-ray absorption analysis of nitrogen contribution to oxygen reduction reaction in carbon alloy cathode catalysts for polymer electrolyte fuel cells

Niwa, Hideharu*; Horiba, Koji*; Harada, Yoshihisa*; Oshima, Masaharu*; Ikeda, Takashi; Terakura, Kiyoyuki*; Ozaki, Junichi*; Miyata, Seizo*

Journal of Power Sources, 187(1), p.93 - 97, 2009/02

 Times Cited Count:381 Percentile:0.15(Chemistry, Physical)

The electronic structure of nitrogens introduced in various carbon-based cathode catalysts for a polymer electrolyte fuel cell (PEFC) has been investigated using X-ray absorption spectroscopy (XAS). The profile of the $$pi^{ast}$$ peaks at the pre-edge of the N 1s XAS spectra is used to determine the chemical states of nitrogens, which can be a marker of the oxygen reduction reaction (ORR) activity; it is found that catalysts that have relatively high amount of graphite-like nitrogen exhibit higher ORR activity than those having relatively high amount of pyridine-like nitrogen. We propose that effective doping of graphite-like nitrogen is a practical guideline for the synthesis of active carbon alloy catalysts.

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