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Origin of improved electrochemical activity of β-MnO2 nanorods: Effect of the Mn valence in the precursor on the crystal structure and electrode activity of manganates

Title
Origin of improved electrochemical activity of β-MnO2 nanorods: Effect of the Mn valence in the precursor on the crystal structure and electrode activity of manganates
Authors
Kim I.Y.Ha H.-W.Kim T.W.Paik Y.Choy J.-H.Hwang S.-J.
Ewha Authors
최진호황성주
SCOPUS Author ID
최진호scopus; 황성주scopus
Issue Date
2009
Journal Title
Journal of Physical Chemistry C
ISSN
1932-7447JCR Link
Citation
vol. 113, no. 51, pp. 21274 - 21282
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
1D nanorods/nanowires of manganese oxides with different crystal structures and morphologies were prepared and characterized to understand the influence of the Mn valence in the solid-state precursor on the electrochemical activity of these nanomaterials and to elucidate the mechanism responsible for the excellent activity of β-MnO2 nanorods as well. According to powder X-ray diffraction analyses, treating manganese oxide precursors that have an oxidation state of ≤+3 with persulfate ions under hydrothermal conditions yields manganese oxides with the β-MnO2 structure. In contrast, the use of a LiMn2O4 precursor with a higher Mn valence leads to the formation of the α-MnO2-structured manganese oxide. Electron microscopic studies clearly show a 1D nanorod-type morphology for the β-MnO2 material, whereas a 1D nanowire-type morphology with a higher aspect ratio is observed for the α-MnO2 material. The diameter of the β-MnO2 nanorods decreases as the Mn valence in the precursors becomes smaller. According to electrochemical measurements, the formation of nanorods dramatically improves the electrode performance of the β-MnO2 phase. This compares with a relatively weak performance enhancement for the α- and δ-MnO2 phases upon the nanowire formation. The optimum electrode property results from the smaller β-MnO2 nanorods prepared with the MnO precursor. 7Li magic angle spinning nuclear magnetic resonance spectroscopy clearly demonstrates that Li+ ions in the lithiated β-MnO2 phase are adsorbed mainly on the sample surface. On the basis of this finding, we attribute the improved electrode performance of the β-MnO2 nanorods to their expanded surface area. © 2009 American Chemical Society.
DOI
10.1021/jp908556h
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자연과학대학 > 화학·나노과학전공 > Journal papers
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