TY - JOUR
T1 - Operando Observations of a Manganese Oxide Electrocatalyst for Water Oxidation Using Hard/Tender/Soft X-ray Absorption Spectroscopy
AU - Tsunekawa, Shun
AU - Yamamoto, Futaba
AU - Wang, Ke Hsuan
AU - Nagasaka, Masanari
AU - Yuzawa, Hayato
AU - Takakusagi, Satoru
AU - Kondoh, Hiroshi
AU - Asakura, Kiyotaka
AU - Kawai, Takeshi
AU - Yoshida, Masaaki
N1 - Funding Information:
This work was performed at the UVSOR Synchrotron (29-207, 28-205, 27-218), PF (2016G647, 2018G589, 2019G674), SPring-8 (2015B1082, 2017B1082, 2019A1386), and the Nano-Fabrication Support Laboratory of Yamaguchi University (JPMXP09F19YA0015, F20YA0006), and was supported by a Grant-in-Aid for Scientific Research (C) (17K05843) from the JSPS, the Electric Technology Research Foundation of Chugoku, and the Cooperative Research Program of Hokkaido University (17B1002, 20B1033). The authors would like to thank K. Yamada, T. Kimura, and Prof. Sakata at Yamaguchi University, T. Ina at JASRI, Prof. Abe and Prof. Amemiya at KEK-PF, and S. Onishi and Y. Mitsutomi at Keio University for experimental support and valuable discussion.
Publisher Copyright:
© 2020 American Chemical Society.
PY - 2020/10/29
Y1 - 2020/10/29
N2 - A layered manganese oxide catalyst containing K+ cations [K/MnOx catalyst] was developed, and its ability to efficiently decompose water was demonstrated. Operando hard/tender/soft X-ray absorption fine structure (XAFS) techniques were used to investigate the function of the K/MnOx catalyst under working conditions. The Mn valency depended on the potential and the amount of K+ cation adsorption. Mn K-edge (hard X-ray) XAFS measurements for the K/MnOx catalyst suggested that the Mn in the catalyst was an Mn3+ species with an octahedral δ-MnO2 structure at a lower electrode potential, which changed reversibly to an Mn4+ species with a δ-MnO2 structure at higher potential during oxygen evolution. A similar result was obtained from operando O K-edge (soft X-ray) XAFS. The chemical state of K species was analyzed using operando K K-edge (tender X-ray) XAFS, which indicated that K+ cations were intercalated with hydrated states in the δ-MnO2 layers. These operando XAFS results demonstrated that the layered δ-MnO2 containing hydrated K+ cations functioned as efficient oxygen evolution electrocatalysts because of the presence of Mn3+ reaction sites.
AB - A layered manganese oxide catalyst containing K+ cations [K/MnOx catalyst] was developed, and its ability to efficiently decompose water was demonstrated. Operando hard/tender/soft X-ray absorption fine structure (XAFS) techniques were used to investigate the function of the K/MnOx catalyst under working conditions. The Mn valency depended on the potential and the amount of K+ cation adsorption. Mn K-edge (hard X-ray) XAFS measurements for the K/MnOx catalyst suggested that the Mn in the catalyst was an Mn3+ species with an octahedral δ-MnO2 structure at a lower electrode potential, which changed reversibly to an Mn4+ species with a δ-MnO2 structure at higher potential during oxygen evolution. A similar result was obtained from operando O K-edge (soft X-ray) XAFS. The chemical state of K species was analyzed using operando K K-edge (tender X-ray) XAFS, which indicated that K+ cations were intercalated with hydrated states in the δ-MnO2 layers. These operando XAFS results demonstrated that the layered δ-MnO2 containing hydrated K+ cations functioned as efficient oxygen evolution electrocatalysts because of the presence of Mn3+ reaction sites.
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U2 - 10.1021/acs.jpcc.0c05571
DO - 10.1021/acs.jpcc.0c05571
M3 - Article
AN - SCOPUS:85096057447
SN - 1932-7447
VL - 124
SP - 23611
EP - 23618
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 43
ER -