Synthesis of monolayers and bilayers of cobalt oxyhydrates (Na,K) x (H2O) y CoO2-δ

Chia Jyi Liu, Chia Yuan Liao, Jiunn Yuan Lin, Jyh Fu Lee

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Abstract

Potassium sodium cobalt oxyhydrates (Na,K)x(H2O)yCoO2-δ were synthesized from -Na0.7CoO2 by using aqueous KMnO4 solution in a one-pot process. Chemical and structural analyses revealed that a partial or even almost complete replacement of K+ for Na+ in the alkaline layers occurs. Direct formation of the c 13.9 phase is apparently associated with the larger size of K+ (1.4 ) as compared to Na+ (1.0 ). Formation of (Na,K)x(H2O)yCoO2-δ not only involves de-intercalation, oxidation and hydration processes, but also an ion exchange reaction. Based on a systematic study, the phase formation of (Na,K)x(H2O)yCoO2-δ with c 19.6 is a slow process, particularly when using aqueous KMnO4 solution with low molar ratio of KMnO4/Na. When comparing the Co K-edge X-ray absorption spectra of (Na,K)x(H2O)yCoO2-δ with those of Nax(H2O)yCoO2 obtained from Br2/CH3CN solution, the edge energy of the main peak of the bilayered hydrate is found to be 3.5 eV higher than that of the monolayered hydrate for (Na,K)x(H2O)yCoO2-δ. In contrast, the edge energy of the main peak of the bilayered hydrate is 0.4 eV lower than that of the monolayered hydrate for Nax(H2O)yCoO2. In addition, the hydration behavior of monolayered of (Na,K)x(H2O)yCoO2-δ is different from that of Nax(H2O)yCoO2. These results seem to suggest that they are two different systems.

Original languageEnglish
Pages (from-to)1585-1597
Number of pages13
JournalPhilosophical Magazine
Volume90
Issue number12
DOIs
Publication statusPublished - 2010 Apr 1

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All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

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