Synthesis, properties, and applications of magnetic iron oxide nanoparticles

Co3O4 nanotubes, nanorods, and nanoparticles are used as the anode materials of lithium-ion batteries. The results show that the Co3O4 nanotubes prepared by a porous-alumina-template method display high discharge capacity and superior cycling reversibility. Furthermore, Co3O4 nanotubes exhibit excellent sensitivity to hydrogen and alcohol, owing to their hollow, nanostructured character.

Co3O4 nanomaterials in lithium-ion batteries and gas sensors

Ultralayered Co3O4 structures with high porosity have been synthesized by a facile homogeneous precipitation process under hydrothermal conditions. The superstructures consist of well-arranged micrometer length rectangular 2D flakes with high specific surface area, pore volume, and uniform pore size distribution. The electrochemical measurements demonstrate that charge storage occurs in ultralayered Co3O4 due to reversible redox reactions. The charge–discharge study shows that the material is capable of delivering very high specific capacitance of 548 F g–1 at a current density of 8 A g–1 and retains 66% of capacitance at 32 A g–1. The charge–discharge stability measurements show excellent specific capacitance retention capability, ca. 98.5% after 2000 continuous charge–discharge cycles at high current density of 16 A g–1. The exceptional cyclic, structural, and electrochemical stability at higher current rate with ∼100% Coulombic efficiency, and very low ESR value from impedance measurements promise good...

Ultralayered Co3O4 for High-Performance Supercapacitor Applications

The present work reports the synthesis and the characterization of cobalt oxide thin films obtained by chemical vapor deposition (CVD) on indium tin oxide (ITO) substrates, using a cobalt(II) β-diketonate as precursor. The complex is characterized by electron impact mass spectrometry (EI-MS) and thermal analysis in order to investigate its decomposition pattern. The depositions are carried out in a cold wall reactor in the temperature range 350−500 °C at different oxygen pressures, to tailor film composition from CoO to Co3O4. The crystalline nanostructure is evidenced by X-ray diffraction (XRD), while the surface and in-depth chemical composition is studied by X-ray photoelectron (XPS) and X-ray excited auger electron spectroscopy (XE-AES). Atomic force microscopy (AFM) is employed to analyze the surface morphology of the films and its dependence on the synthesis conditions. Relevant results concerning the control of composition and microstructure of Co−O thin films are presented and discussed.

Composition and Microstructure of Cobalt Oxide Thin Films Obtained from a Novel Cobalt(II) Precursor by Chemical Vapor Deposition

A Co(OH)(2)/zeolite nanocomposite with an extraordinarily high specific capacitance is described. Nanometer-sized Co(OH)(2) whiskers on the zeolite surface permit high electrochemical accessibility and a fast diffusion rate of electrolyte through the material, resulting in a specific capacitance approaching the theoretical limit. increasing the Co(OH)(2) loading increases whisker growth (see Figure), until bulk Co(OH)(2) begins to nucleate and grow in solution (arrows).

Preparation of the Novel Nanocomposite Co(OH)2/ Ultra‐Stable Y Zeolite and Its Application as a Supercapacitor with High Energy Density

Thin films of the cubic spinel Co{sub 3}O{sub 4} were prepared by the sol-gel route from a Co(II) sulfate precursor using a dip-coating technique. The films (50 to 60 nm thick) were deposited on indium-tin oxide glass substrates with a single dipping. The electrochromic properties of the films were studied in an aqueous alkaline electrolyte (0.1 M LiOH) using cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. The intermediate oxide products that appeared during cycling at current peak potentials were analyzed by x-ray diffraction (XRD) and ex situ Fourier transform infrared (FTIR) reflection-absorption spectroscopy performed at near-grazing incidence angle conditions (NGIA). High hydration of the spinel structure enables complex redox processes to take place inside the structure or on the surface of the film when potential cycling is performed. Vibrational bands characteristic of the formation of CoO, Co(OH){sub 2}, and hydrated Co{sub 3}O{sub 4} phases have been assigned and discussed according to the results obtained from ex situ NGIA FTIR, CV, and XRD studies. The change in transmittance ({lambda} = 634 nm) between bleached and colored states for single-dipped films was 25%, and for electrochromic efficiency ({eta}) was approximately 25 cm{sup 2}/C.

Structural and Spectroelectrochemical Investigations of Sol-Gel Derived Electrochromic Spinel Co[sub 3]O[sub 4] Films

Electrochromism of iron oxide films prepared via the sol-gel route by the dip-coating technique

Spectroelectrochemical and structural properties of electrochromic Co(Al) -oxide and Co(Al,Si) -oxide films prepared by the sol-gel route

New electrochromic spinel-type Co(Al)-oxide and Co(Al,Si)-oxide films exhibiting coloring/bleaching changes ΔT= Tcolored−T bleached = 75% − 25% = 50% (where T is transmittance) with a coloring efficiency of 22cm2 C−1 were deposited by a dip-coating method from aqueous colloidal solutions made by thermal hydrolysis of Co(II)-acetate, Al(III)-sulphate, citric acid and 3-aminopropyltriethoxysilane precursors. The nanocomposite spinel structure of the films and powders was determined using X-ray diffraction, thermogravimetry, visible and infrared transmission and reflection-absorption spectroscopy performed at near-grazing incidence angle conditions (80°) using p-polarized light. The existence of spinel lattice modes in the IR spectra of cycled films proved that the spinel structure of Co(Al,Si)-oxide films is preserved at least on the scale of short-range interactions detected with IR spectroscopy. In addition to this, sulphate (SO42−) ions are retained in the structure of cycled films heat-treated at 500 °C. The role of order-disorder transitions of sulphate ions present in cycled films is discussed with respect to their influence in enhancing the speed and degree of coloring/bleaching changes of electrochromic Co(Al,Si)-oxide spinel films.

F. Švegl

Papers

Structural and Spectroelectrochemical Investigations of Sol-Gel Derived Electrochromic Spinel Co[sub 3]O[sub 4] Films

Electrochromism of iron oxide films prepared via the sol-gel route by the dip-coating technique

Spectroelectrochemical and structural properties of electrochromic Co(Al) -oxide and Co(Al,Si) -oxide films prepared by the sol-gel route

Spectroelectrochemical and Structural Properties of Electrochromic Co( Al)‐Oxide and Co(Al,Si)‐Oxide Films Prepared by the Sol‐Gel Route.