Effect of Temperature on Structure and Electronic Properties of Nanometric Spinel-Type Cobalt Oxides

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• 作者：G. Godillot ; L. Guerlou-Demourgues ; L. Croguennec ; K. M. Shaju ; C. Delmas
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：May 9, 2013
• 年：2013
• 卷：117
• 期：18
• 页码：9065-9075
• 全文大小：480K
• 年卷期：v.117,no.18(May 9, 2013)
• ISSN：1932-7455

文摘

Temperature is shown to have a huge influence on the electronic properties of nanometric spinel-type cobalt oxides precipitated at low temperature in alkaline media. The initial phase, with formula H_xLi_yCo_{3鈭捨?/sub>O4, contains hydrogen, lithium, cobalt vacancies, and a mixed valence Co⁴⁺/Co³⁺ within the structure, leading to an electronic conductivity higher than that of stoichiometric Co3O4. Its structural evolution under thermal treatment was studied by X-ray diffraction and chemical analysis, which reveal modifications in structure and compositions, involving water release, increase of the Co/O atomic ratio, and modification of the Co⁴⁺/Co³⁺ ratio. The RT to 300 掳C range is particularly interesting as a single-phase domain and the materials obtained in this temperature range were investigated by chemical analysis, electronic conductivity and specific surface area measurements. Upon increasing temperature, the enhancement of the Co⁴⁺/Co³⁺ ratio, together with cationic redistribution in the spinel framework, results in an improvement of the electronic conductivity (more than 2 orders of magnitude for materials heated above 150 掳C). Finally, the systematic thermal study of electronic conductivity and specific surface area of the materials allows to determine an optimal heat-treatment temperature leading to an optimized active electrode material for electrochemical energy storage applications, especially in supercapacitors. Such a solid state chemistry approach combining many material characterization techniques to reach a complete knowledge of the material is quite rare in the literature concerning oxides for supercapacitors.}