J. Mosa

Preparation of Li4Ti5O12 electrode thin films by a mist CVD process with aqueous precursor solution

Abstract Spinel Li4Ti5O12 thin films were prepared by a mist CVD process, using an aqueous solution of lithium nitrate and a water-soluble titanium lactate complex as the source of Li and Ti, respectively. In this process, mist particles ultrasonically atomized from a source aqueous solution were transferred by nitrogen gas to a heating substrate to prepare thin films. Scanning electron microscopy observation showed that thin films obtained by this process were dense and smooth, and thin films with a thickness of about 500 nm were obtained. In the X-ray diffraction analysis, formation of Li4Ti5O12 spinel phase was confirmed in the obtained thin film sintered at 700 °C for 4 h. The cell with the thin films as an electrode exhibited a capacity of about 110 mAh g−1, and the cell showed good cycling performance during 10 cycles.

Hybrid Materials for High Ionic Conductivity

Organic–inorganic hybrid materials are a blending of two components where at least one of them is at the nanoscale. The sol-gel process is an interesting method to synthesize these materials because it allows a wide variation in compositions and inorganic/organic ratios, together with an excellent control of porosity (volume, size and connectivity) and functional groups. These features enable the design of hybrid materials with high ion conductivity for different applications as electrolytes for proton exchange membranes fuel cells (PEMFC) and lithium ion batteries. Two of the main constraints of PEMFC are the operation conditions, limited to maximum temperatures of 80°C and relative humidity near 100%. Increasing of operation temperature above 100°C is a highly desirable goal because it increases the electrochemical kinetics, improves CO tolerance, facilitates heat rejection, and reduces the problems associated with water management. Although some of the properties have been achieved separately, no system has been able to gather all the necessary requirements. In the case of application of hybrid materials as solid electrolytes for lithium ion batteries, the ion conductivity is only slightly improved compared with poly(ethylene oxide)-based polymer electrolytes and still far from values of organic liquids. Besides, in the field of microbatteries, the electrolyte thickness can be as low as one micron, and, in this configuration, ionic conductivities of 10−5 S/cm or higher would be enough for practical applications.

Transparent SiO2-GdF3 sol–gel nano-glass ceramics for optical applications

AbstractTransparent oxyfluoride nano-glass-ceramics (GCs) containing GdF3 nanocrystals undoped and doped with 0.5 Eu3+ (mol%) were obtained by a novel sol–gel method after sintering at temperatures such low as 550 °C. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) show the precipitation of GdF3 nanocrystals with size between 7 and 10 nm, depending on the crystalline phase (hexagonal or orthorhombic) and the heating time. Fourier transform infrared spectroscopy (FTIR) analysis allows following the system evolution during the heat treatment showing the decomposition of trifluoroacetic acid (TFA), used as fluorine precursor, together with the formation of fluoride lattice bonding. Energy dispersive X-ray (EDX) analysis confirms the incorporation of the RE ions in the fluoride nanocrystals in the GCs. The ions incorporation on the GdF3 crystals is also supported by optical characterisation. Photoluminescence measurements result in a well resolved structure together with a narrowing of the Eu3+ emission and excitation spectra in the GCs compared to the xerogel. Moreover, the asymmetry ratio between the electric dipole transition (5D0→7F2) to the magnetic dipole transition (5D0→7F1) is reduced in GCs, indicating that Eu3+ ions are incorporated in the GdF3 crystalline phases. Moreover, Gd3+→Eu3+ energy transfer with enhancement of the energy transfer efficiency was observed in the GCs, further supported by fluorescence decay curves. HighlightsEu3+ doped SiO2-GdF3 GCs with 20 mol% of crystalline phase has been successfully obtained by sol–gel method.The use of methyl triethoxysilane allows obtaining crack-free GCs samples and reduces the hydroxyl groups.Energy transfer with enhancement of efficiency was observed from Gd3+ to Eu3+ in the nanocrystals.

Electrochemical characterization of sol–gel coatings for corrosion protection of metal substrates

AbstractInorganic and hybrid organic–inorganic sol–gel coatings are one of the most interesting alternatives for the corrosion protection of metallic substrates based on the design possibilities offered by this processing method. These include the ability to combine the barrier function between the metal and the surrounding environment, and the self-healing effect by the incorporation of corrosion inhibitors into the coating itself. Electrochemical characterization is essential for the study of the corrosion process, and the techniques used are based on the movement of electric charges that takes place during the corrosion process. Some of these techniques perform measurements on a relatively large area of the coated metal, obtaining average results of the corrosion characteristics. The main techniques belonging to this group are electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP). However, they do not provide details on the location of anodes, cathodes or defects. Other local electrochemical techniques are used to provide this type of information, necessary in many cases to determine the exact mechanism of protection offered by the coatings: scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET), scanning Kelvin probe technique (SKP) and localized electrochemical impedance spectroscopy (LEIS). In this paper, a brief review of the particularities of these techniques in their application to sol–gel coatings on metals is included. The main part of the paper is focused on the analysis of some of the most representative examples of the application of these electrochemical techniques, trying to analyze different metal alloys. Combination of electrochemical techniques is essential to accurately analyze the corrosion protection mechanism of sol–gel coatings, including passive and active protection, ion diffusion, delamination, etc.HighlightsCorrosion protection using sol–gel coatings has been enhanced based on the design improvement.Combination of electrochemical techniques for a precise evaluation of the protection mechanism.SKP and OCP measurements are very promising electrochemical techniques for the corrosion analysis.Influence of corrosion products on electrochemical results should be analyzed in a greater detail.