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

Abstract

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 x Li y Co 3−δ O 4 , contains hydrogen, lithium, cobalt vacancies, and a mixed valence Co 4+ /Co 3+ within the structure, leading to an electronic conductivity higher than that of stoichiometric Co 3 O 4 . 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 Co 4+ /Co 3+ ratio. The RT to 300 °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 Co 4+ /Co 3+ 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 °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.

High power density aqueous hybrid supercapacitor combining activated carbon and highly conductive spinel cobalt oxide

“…These phases, which were synthesized by oxidizing precipitation of cobalt nitrate in a basic medium (T < 90 C), exhibit a modified spinel -Co 3 O 4 type structure, with protons, lithium and cobalt vacancies, as well as Co 4þ ions in the octahedral trivalent cobalt network [4e6]. Such octahedral tetravalent cobalt ions entail electronic delocalization and very good electronic conductivity properties (5 Â 10 À4 S cm À1 , against 10 À6 S cm À1 for ideal Co 3 O 4 ), which can still be improved by a controlled thermal treatment at a moderate temperature (200 C), while keeping particle size and specific surface area (200 m 2 g À1 ) suitable for electrochemical cycling [5,6].…”

Optical absorption induced by small polaron formation in transition metal oxides: The case ofCo3O4

“…In order to verify our hypothesis and to further elucidate the role of polaron formation, we calculated the optical absorption spectra of Co 3 O 4 with and without a hole polaron, and we compared the results with available experimental data. Absorption spectrum with a hole polaron was computed with a 56-atom supercell [75], which better represents experimental hole concentrations of p-type Co 3 O 4 [42,44] due to abundant cation vacancies [55,76].…”

Synthesis and Identification of Co3O4·Fe3O4/CaO Spinel Supported Catalyst

“…The results of elemental analysis of cobalt, iron and calcium in the prepared catalyst prepared at different temperatures (450, 650 and 800 ºC) are shown in Table-2. Table-2 The XRD and all spectroscopic studies results proved that the supported spinel catalyst Co 3 O 4 •Fe 3 O 4 /CaO begin to form at low temperature 450 ºC and completed at 650 ºC by using co-precipitation method and then began to convert to CoFe 2 O 4 /CaO and FeCo 2 O 4 /CaO spinel type at 800 ºC because of the increasing of dispersion of catalyst component oxides in each other with the increasing of calcination temperatures [44].…”