title: Nitrogen-Rich Manganese Oxynitrides with Enhanced Catalytic Activity in the Oxygen Reduction Reaction.
abstract: The catalytic activity of manganese oxynitrides in the oxygen reduction reaction (ORR) was investigated in alkaline solutions to clarify the effect of the incorporated nitrogen atoms on the ORR activity. These oxynitrides, with rock-salt-like structures with different nitrogen contents, were synthesized by reacting MnO, Mn2 O3 , or MnO2 with molten NaNH2 at 240-280 °C. The anion contents and the Mn valence states were determined by combustion analysis, powder X-ray diffraction, and X-ray absorption near-edge structure analysis. An increase in the nitrogen content of rock-salt-based manganese oxynitrides increases the valence of the manganese ions and reinforces the catalytic activity for the ORR in 1 m KOH solution. Nearly single-electron occupancy of the antibonding eg states and highly covalent Mn-N bonding thus enhance the ORR activity of nitrogen-rich manganese oxynitrides.
authors.affiliation: Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, 060-0808, Japan. amiura@eng.hokudai.ac.jp.
authors.forename: Akira
authors.initials: A
authors.lastname: Miura
authors.affiliation: Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, 060-0808, Japan.
authors.forename: Carolina
authors.initials: C
authors.lastname: Rosero-Navarro
authors.affiliation: Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, 060-0808, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Masubuchi
authors.affiliation: Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, 060-0808, Japan.
authors.forename: Mikio
authors.initials: M
authors.lastname: Higuchi
authors.affiliation: Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, 060-0808, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kikkawa
authors.affiliation: Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, 060-0808, Japan.
authors.forename: Kiyoharu
authors.initials: K
authors.lastname: Tadanaga
keywords: manganese; nitrides; oxygen reduction; oxynitrides