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Formation and oxidation of nanosized metal particles by electrochemical reaction of Li and Na with NiCo2O4: X-ray absorption spectroscopic study

Chadwick, Alan V. and Savin, Shelley L. P. and Fiddy, Steven and Alcantara, Ricardo and Fernandez Lisbona, Diego and Lavela, Pedro and Ortiz, Gregorio F. and Tirado, Jose L. (2007) Formation and oxidation of nanosized metal particles by electrochemical reaction of Li and Na with NiCo2O4: X-ray absorption spectroscopic study. JOURNAL OF PHYSICAL CHEMISTRY C, 111 (12). pp. 4636-4642.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jp077427d

Abstract

X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy have been used to investigate the electrochemical reactions of NiCo2O4 in lithium and sodium test cells. Nanosized particles of NiCo2O4 were prepared by the thermal decomposition of a mixed oxalate precursor and used as active electrode material. Ni K and Co K XANES results give evidence of the successive steps in the reduction mechanism of the oxide during the first cell discharge. In a first step NiCo2O4 reacts with lithium and sodium and the reduction of both Ni3+ and Co3+ to the 2+ oxidation state is shown by a peak shift to lower energy values. As a result, sodium oxide or lithium oxide and the transition metal monoxides are formed. Second, metallic products are formed, in which the average coordination numbers of the nearest neighbors for Ni and Co derived from the EXAFS data are 4 and 5, respectively, associated with ca. 1 nm particle size. These novel ultrafine particles are stabilized in the Li2O matrix of the discharged electrodes. Reoxidation of the metallic products up to a divalent state of Ni and Co in the form of monoxides is achieved during the charge process of the electrochemical cells.

Item Type:Article
Subjects:Material Science > Functional and hybrid materials
Material Science > Nanofabrication processes and tools
Material Science > Nanochemistry
ID Code:3276
Deposited By:Farnush Anwar
Deposited On:15 Jan 2009 13:57
Last Modified:27 Jan 2009 15:45

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