Superionic Conduction in Co-Vacant P2-Nax CoO2 Created by Hydrogen Reductive Elimination.
The layered P2-Nax MO2 (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2-Nax CoO2 created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm(-1) at 25 °C. Using in situ synchrotron X-ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na0.61 (H3 O)0.18 Co0.93 O2 . Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co-stoichiometric compound Nax (H3 O)y CoO2 does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity.
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan. katok@spring8.or.jp.|CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan. katok@spring8.or.jp.
Kenichi
K
Kato
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.|CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.|Faculty of Pure and Applied Sciences, TIMS, CiRfSE, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8571, Japan.
Hidetaka
H
Kasai
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.|Institute for Integrated Cell-Material Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto, 606-8501, Japan.
Akihiro
A
Hori
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.|Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
Masaki
M
Takata
Department of Materials Science, Shimane University, 1060 Nishi-kawatsu-cho, Matsue, Shimane, 690-8504, Japan.
Hiroshi
H
Tanaka
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.|Institute for Integrated Cell-Material Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto, 606-8501, Japan.
Susumu
S
Kitagawa
Graduate School of Engineering, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan.
Akira
A
Kobayashi
CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.|Graduate School of Engineering, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan.|Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
Nobuki
N
Ozawa
Graduate School of Engineering, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan.|Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
Momoji
M
Kubo
CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.|Department of Chemistry and Bioengineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate, 020-8551, Japan.
Hidekazu
H
Arikawa
CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.|Department of Chemistry and Bioengineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate, 020-8551, Japan.
Tatsuya
T
Takeguchi
CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.|International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan.
Masaaki
M
Sadakiyo
CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.|International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan.
Miho
M
Yamauchi
X-ray diffraction; layered compounds; molecular dynamics; reductive elimination; superionic conductivity