A hierarchical, nanoporous TiO 2 structure is successfully prepared by a simple in situ hydrolysis method. Used as an anode material, it achieves a sustained high lithium storage performance especially at high charge/discharge rates due to its substantially high surface area. The material shows two different major storage modes: a) bulk insertion, and b) pseudo-capacitive interfacial storage, which is responsible for 64% of the total capacity. In order to kinetically emphasize the interfacial storage even further, we cycle the material directly at high rates, giving 302 mA h g − 1 and 200 mA h g − 1 of fully reversible discharge capacity at charge/discharge rates of 1 C and 5 C with very high cycle stability. We propose an overall view on the different Li insertion mechanisms of the high-surface-area nanoporous TiO 2 and emphasize the importance of interfacial storage for electrode applications in Li-ion batteries.

The interest of exploring environmentally benign and safe anode materials for lithium batteries has led to TiO 2 (anatase) nanostructures as promising candidates. However, the poor chemical diffusion of lithium in the materials still limits the rate capability. We report on the high rate capability of lithium storage with oxygen-deficient TiO 2−δ nanoparticles prepared by hydrogen reduction. A systematic study on the effect of electronic charge carrier concentration on the overall electrochemical lithium storage performance revealed that well-balanced Li + /e − transport is the key factor for high-performance TiO 2 anodes.

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Insulator-metal transitions are well known in transition metal oxides, but inducing an insulator-metal transition in the oxide of a main group element is a major challenge. Here we report the observation of an insulator-metal transition, with a conductivity jump of seven orders of magnitude, in highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO 1.2 at a temperature around 670 K. We demonstrate through experimental studies and density-functional-theory calculations that the conductivity jump takes place at a critical gallium concentration and is induced by crystallization of stoichiometric Ga 2 O 3 within the metastable oxide matrix -in chemical terms by a disproportionation. This novel mechanism -an insulator-metal transition driven by a heterogeneous solid state reactionopens up a new route to achieve metallic behaviour in oxides that are expected to exist only as classic insulators.Insulator-metal transitions belong to the most fascinating phenomena in condensed-matter physics 1,2 . Since Mott's landmark work 3,4 it has been known that in crystalline solids strong electron-electron interactions can cause an insulator-metal transition. One example is crystalline Cr-doped vanadium oxide, (V 1-x Cr x ) 2 O 3 , which shows a Mott transition from a paramagnetic Mott insulator to a strongly correlated metal upon an increase in pressure, a lowering of temperature, or a decrease in dopant level 5,6 . In non-crystalline solids structural disorder can also lead to an insulator-metal transition on account of Anderson localization 7 .As shown by Anderson 7 and Mott 8 , in any non-crystalline material the lowest states in the conduction band are localized, i.e. they are electron traps. Only for energies above the mobility edge, E c , do states become non-localized or extended. If the Fermi energy E F is below the mobility edge, states at the Fermi level are localized and the material is an electronic insulator. If, however, the number of electrons increases and the Fermi energy rises above the mobility edge, the material becomes metallic (Anderson transition). As transition metals change their valence state easily, most examples of insulator-metal transitions concern transition metal compounds 4-6,9-11 . The above considerations do not, however, exclude the possibility of inducing an insulator-metal transition in a simple binary oxide of a main group element, even without doping. Instead, large deviations from the ideal stoichiometry, i.e. high defect concentrations, provide a high concentration of electronic defects (self-doping). And if, in addition, the oxide is amorphous, there are two phenomena, strong structural disorder and strong chemical disorder, which could result in an insulator-metal transition.Here we report such a case: Highly non-stoichiometric, amorphous gallium oxide with an approximate chemical composition GaO 1.2 shows an unprecedented insulator-metal transition, with a jump in conductivity of ca. 7 orders of magnitude at temperatures as high as 670 K. We show that this in...

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The major objective of this research project was to reach a microscopic understanding of the structure, function and dynamics of V-Mo-(W) mixed oxides for the partial oxidation of acrolein to acrylic acid. Different model catalysts (from binary and ternary vanadium molybdenum oxides up to quaternary oxides with additional tungsten) were prepared via a solid state preparation route and hydrochemical preparation of precursors by spray-drying or crystallisation with subsequent calcination. The phase composition was investigated ex situ by XRD and HR-TEM. Solid state prepared samples are characterised by crystalline phases associated to suitable phase diagrams. Samples prepared from crystallised and spray-dried precursors show crystalline phases which are not part of the phase diagram. Amorphous or nanocrystalline structures are only found in tungsten doped samples. The kinetics of the partial oxidation as well as the catalysts' structure have been studied in situ by XAS, XRD, temperature programmed reaction and reduction as well as by a transient isotopic tracing technique (SSITKA). The reduction and re-oxidation kinetics of the bulk phase have been evaluated by XAS. A direct influence not only of the catalysts' composition but also of the preparation route is shown. Altogether correlations are drawn between structure, oxygen dynamics and the catalytic performance in terms of activity, selectivity and long-term stability. A model for the solid state behaviour under reaction conditions has been developed. Furthermore, isotope exchange experiments provided a closer image of the mechanism of the selective acrolein oxidation. Based on the in situ characterisation in combination with micro kinetic modelling a detailed reaction model which describes the oxygen exchange and the processes at the catalyst more precisely is discussed.

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LiFePO 4 is one of the most frequently studied positive electrode materials for lithium-ion batteries during the last years. Nevertheless, there is still an extensive debate on the mechanism of phase transformation. On the one hand this is due to the small energetic differences involved and hence the great sensitivity with respect to parameters such as size and morphology. On the other hand this is due to the lack of in situ observations with appreciable space and time resolution. Here we present scanning transmission X-ray microscopy measurements following in situ the phase boundary propagation within a LiFePO 4 single crystal along the (010) orientation during electrochemical lithiation/delithiation. We follow, on a battery-relevant timescale, the evolution of a two-phase-front on a micrometre scale with a lateral resolution of 30 nm and with minutes of time resolution. The growth pattern is found to be dominated by elastic effects rather than being transport-controlled.