Effect of N, C and B interstitial atoms on local bonding structure in mechanically activated TiH2/h-BN, TiH2/C, and TiH2/B mixtures

Mechanically activated TiH2/h-BN, TiH2/C and TiH2/B mixtures was studied by temperature-programmed desorption, X-ray diffraction, transmission electron microscopy and X-ray emission spectroscopy. Ball milling in the presence of additives results in a modification of hydrogen occupation sites. Additional Ti-N, Ti-C or Ti-B bonds from chemical bonding of Ti with interstitial N, C and B atoms, are formed in TiH2 due to contact of TiH2 nanoparticles with the respective additive matrix materials. Mixed configurations around Ti atoms with proportional combination of local Ti-H and Ti-N, Ti-C or Ti-B bonds significantly decrease the thermal stability of TiH2. The effect is most pronounced when boron is the additive. (C) 2008 Elsevier B.V. All rights reserved

Effect of h-BN additive on hydrogen sorption by Ti under mechanical treatment in H-2/He flow

The effect of h-BN additive on hydrogen sorption by Ti under mechanical treatment in H-2/He flow and on the thermal stability of Ti-hydride produced during milling were studied using kinetic, structural, microscopic, and spectroscopic techniques and theoretical first-principles calculations. The results obtained were compared with the corresponding properties of pure Ti and Ti with graphite additive. Like graphite, hexagonal BN was found to be an effective additive to improve the hydrogen sorption capacity of Ti. New types of occupation sites available for hydrogen, very similar to those detected for Ti/C, were observed. These sites are characterized by a low H-2 desorption temperature: 630-670 K instead of similar to 1000 K

Linking the HOMO-LUMO gap to torsional disorder in P3HT/PCBM blends

The electronic structure of [6,6]-phenyl C61 butyric acid methyl ester (PCBM), poly(3-hexylthiophene) (P3HT), and P3HT/PCBM blends is studied using soft X-ray emission and absorption spectroscopy and density functional theory calculations. We find that annealing reduces the HOMO-LUMO gap of P3HT and P3HT/PCBM blends, whereas annealing has little effect on the HOMO-LUMO gap of PCBM. We propose a model connecting torsional disorder in a P3HT polymer to the HOMO-LUMO gap, which suggests that annealing helps to decrease the torsional disorder in the P3HT polymers. Our model is used to predict the characteristic length scales of the flat P3TH polymer segments in P3HT and P3HT/PCBM blends before and after annealing. Our approach may prove useful in characterizing organic photovoltaic devices in situ or even in operando

Asymmetric pathways in the electrochemical conversion reaction of NiO as battery electrode with high storage capacity

Electrochemical conversion reactions of transition metal compounds create opportunities for large energy storage capabilities exceeding modern Li-ion batteries. However, for practical electrodes to be envisaged, a detailed understanding of their mechanisms is needed, especially vis-à-vis the voltage hysteresis observed between reduction and oxidation. Here, we present such insight at scales from local atomic arrangements to whole electrodes. NiO was chosen as a simple model system. The most important finding is that the voltage hysteresis has its origin in the differing chemical pathways during reduction and oxidation. This asymmetry is enabled by the presence of small metallic clusters and, thus, is likely to apply to other transition metal oxide systems. The presence of nanoparticles also influences the electrochemical activity of the electrolyte and its degradation products and can create differences in transport properties within an electrode, resulting in localized reactions around converted domains that lead to compositional inhomogeneities at the microscale.Published versio