Wet-Chemical Synthesis of 3D Stacked Thin Film Metal-Oxides for All-Solid-State Li-Ion Batteries.

By ultrasonic spray deposition of precursors, conformal deposition on 3D surfaces of tungsten oxide (WO₃) negative electrode and amorphous lithium lanthanum titanium oxide (LLT) solid-electrolyte has been achieved as well as an all-solid-state half-cell. Electrochemical activity was achieved of the WO₃ layers, annealed at temperatures of 500 °C. Galvanostatic measurements show a volumetric capacity (415 mAh·cm-3) of the deposited electrode material. In addition, electrochemical activity was shown for half-cells, created by coating WO₃ with LLT as the solid-state electrolyte. The electron blocking properties of the LLT solid-electrolyte was shown by ferrocene reduction. 3D depositions were done on various micro-sized Si template structures, showing fully covering coatings of both WO₃ and LLT. Finally, the thermal budget required for WO₃ layer deposition was minimized, which enabled attaining active WO₃ on 3D TiN/Si micro-cylinders. A 2.6-fold capacity increase for the 3D-structured WO₃ was shown, with the same current density per coated area

Growth, structural and plasma illumination properties of nanocrystalline diamond-decoratedgraphene nanoflakes

Decorating graphene nanoflakes with nanocrystalline diamond gives superior functioning for microplasma devices with long lifetime stability plasma illumination performances.</p

The impact of bead milling on the thermodynamics and kinetics of the structural phase transition of VO2 particulate materials and their potential for use in thermochromic glazing

The thermodynamics and kinetics of the structural phase transition from monoclinic VO2 (M) to rutile VO2 (R) and vice versa were studied for particulate materials obtained by bead milling of VO2 (M) powder. Using wet bead milling, we decreased the particle size of VO2 (M) powder from ∼1 μm to 129 nm. With progressive milling, the switching enthalpy decreased from 47 J g−1 to 29 J g−1 due to a loss of crystallinity. The switching kinetics were studied using Friedman's differential isoconversional method. The activation energy |Eα| decreases with increasing difference between the actual temperature of the material and its switching temperature (T0). Furthermore, |Eα| decreases with progressive milling, and kinetic asymmetry is induced. For milled particulate materials, |Eα| is lower for the switch from VO2 (R) to VO2 (M) than for the opposite switch. For hydrothermally synthesized nanoparticles, |Eα| is in the same order of magnitude, albeit with inverse switching asymmetry. Latter may result from different defects that are introduced during both preparation techniques. Applying layers of milled particulate material to glass sheets yielded thermochromic coatings with luminous transmission of 40.7% and solar modulation of 8.3%. This demonstrates that milled VO2 particles have potential for use in energy efficient thermochromic windows

Arsenic release during pyrolysis of CCA treated wood waste: current state of knowledge

Low-temperature pyrolysis is evaluated as a possible technique for the disposal of chromated copper arsenate (CCA) treated wood waste. Theoretical and experimental studies are performed in order to gain more insight in the mechanism of arsenic release. In this paper, the most important observations and results of modelling are brought together in order to present the current state of knowledge. Lab-scale pyrolysis experiments show that pyrolysis at 300 °C for 20 min gives rise to inconclusive release for the three metals. However, arsenic releases are substantial for all experiments using a temperature of 320 °C. A speciation study shows the presence of trivalent arsenic in the pyrolysis residue, indicating that arsenic, present in pentavalent state in the CCA solution and in the CCA treated wood, is partly reduced to the trivalent state during pyrolysis. Arsenic release can be modelled by a simple first order single-reaction kinetic scheme for the temperature range from 350 to 450 °C. Based on the order of magnitude of the kinetic constants, the reaction is identified as a reduction reaction. Thermogravimetric (TG) analysis of hydrated chromium arsenate (the major arsenic compound in CCA treated wood) reveals that thermal decomposition probably results in the formation of solid Cr2O3 and gaseous H2O, O2 and As4O6, indicating again that As(V) is reduced to As(III) and arsenic is released in trivalent form. TG studies of the pure arsenic oxides (As2O5 and As2O3) show that at temperatures lower than 500 °C the reduction reaction As2O5→As2O3+O2 does not take place. At higher temperatures decomposition is observed. As2O3, however, is already released at temperatures as low as 200 °C. This release is driven by temperature dependent vapour pressures. It can be concluded that the wood, char and pyrolysis vapours form a reducing environment, thereby influencing the thermal behaviour of the arsenic oxides. An other explanation for the difference in thermal behaviour could be that part of the arsenic in the CCA treated wood is already present in the trivalent form.status: publishe

Effect of annealing atmosphere on LiMn2O4 for thin film Li-ion batteries from aqueous chemical solution deposition

In this study we demonstrate and explain the direct relationship between precursor chemistry and phase formation of LiMn2O4 powders and thin films from aqueous chemical solution deposition (CSD). The processing conditions applied to transform the precursor into the LiMn2O4 phase are investigated with a focus on the heating atmosphere and temperature. We found that the Mn2+ ions, used as a starting product, already partially oxidize into Mn3+/Mn4+ in the precursor solution. The Mn3+ ions present in the gel or the dried film are extremely sensitive to O-2, leading to fast oxidation towards Mn4+. Here, we suggest that the oxygen, introduced in the precursor solution by the citrate complexing agent, suffices to oxidize the Mn2+ into Mn3+/Mn4+ which is crucial in the formation of phase pure spinet and stoichiometric LiMn2O4. Any additional oxygen, available as O-2 during the final processing, should be avoided as it leads to further oxidation of the remaining Mn3+ into Mn4+ and to the formation of the gamma-Mn2O3 and lambda-MnO2 secondary phases. Based on these insights, the preparation of phase pure, spinet and stoichiometric LiMn2O4 in a N-2 ambient was achieved both in powders and films. Moreover, the study of the precursor chemistry and final annealing leads to the possibility of reducing the final temperature to 450 degrees C, enabling the use of temperature and oxidation sensitive current collectors such as TiN. This inert ambient and low temperature processing of LiMn2O4 provides the opportunity to have large flexibility and compatibility with process conditions for other materials in the thin film battery stack, without undesired oxidations

3D indium tin oxide electrodes by ultrasonic spray deposition for current collection applications

Three dimensionally (3D) structured indium tin oxide (ITO) thin films are synthesized and characterized as a 3D electrode material for current collection applications. Using metal citrate chemistry in combination with ultrasonic spray deposition, a low cost wet-chemical method has been developed to achieve conformal ITO coatings on non-planar scaffolds. Although there is room for improvement with respect to the resistivity (9.9·10−3 Ω∙cm, 220 nm thick planar films), high quality 3D structured coatings were shown to exhibit conductive properties based on ferrocene reactivity. In view of applications in Li-ion batteries, the electrochemical stability of the current collector was investigated, indicating that stability is guaranteed for voltages of 1.5 V and up (vs. Li+/Li). In addition, subsequent 3D coating of the ITO with WO3 as a negative electrode (battery) material confirmed the 3D ITO layer functions as a proper current collector. Using this approach, an over 4-fold capacity increase was booked for 3D structured WO3 in comparison to planar samples, confirming the current collecting capabilities of the 3D ITO coating. Therefore, the 3D ITO presented is considered as a highly interesting material for 3D battery applications and beyond

Generalized approach to the description of recombination kinetics in bulk heterojunction solar cells-extending from fully organic to hybrid solar cells

Lately, research efforts in photovoltaics towards hybrid solar cells based on nanostructured metal oxides and conjugated polymers have been intensifying. However, very limited effort has been spent so far to investigate their recombination kinetics in comparison with their fully organic counterpart. In this work, impedance spectroscopy under different illumination intensities is used to probe the recombination kinetics of hybrid solar cells based on ZnO nanorod arrays and poly(3-hexylthiophene). A recombination-based model developed for fully organic solar cells is effectively applied in our hybrid solar cells, demonstrating their similarity in device physics and establishing the nanorod array/polymer compound as true bulk heterojunction. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4714902