Ti K-edge x-ray absorption near edge spectroscopy (XANES) was used to explore the Ti valence and coordination in Ti-activated sodium alanate. An empirical relationship was established between the Ti valence and the Ti K-edge onset based on a set of standards. This relationship was used to estimate oxidation states of the titanium catalyst in 2 mol% and 4 mol% Ti-doped NaAlH4. These results demonstrate that the formal titanium valence is zero in doped sodium alanate and nearly invariant during hydrogen cycling. A qualitative comparison of the edge fine structure suggests that the Ti is present on the surface in the form of amorphous TiAl3.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let

We report the results of an experimental and theoretical study of hydrogen storage in sodium alanate (NaAlH(4)). Reversible hydrogen storage in this material is dependent on the presence of 2-4% Ti dopant. Our combined study shows that the role of Ti may be linked entirely to Ti-containing active catalytic sites in the metallic Al phase present in the dehydrogenated NaAlH(4). The EXAFS data presented here show that dehydrogenated samples contain a highly disordered distribution of Ti-Al distances with no long-range order beyond the second coordination sphere. We have used density functional theory techniques to calculate the chemical potential of possible Ti arrangements on an Al(001) surface for Ti coverages ranging from 0.125 to 0.5 monolayer (ML) and have identified those that can chemisorb molecular hydrogen via spontaneous or only moderately activated pathways. The chemisorption process exhibits a characteristic nodal symmetry property for the low-barrier sites: the incipient doped surface-H(2) adduct's highest occupied molecular orbital (HOMO) incorporates the sigma antibonding molecular orbital of hydrogen, allowing the transfer of charge density from the surface to dissociate the molecular hydrogen. This work also proposes a plausible mechanism for the transport of an aluminum hydride species back into the NaH lattice that is supported by Car-Parrinello molecular dynamics (CPMD) simulations of the stability and mobility of aluminum clusters (alanes) on Al(001). As an experimental validation of the proposed role of titanium and the subsequent diffusion of alanes, we demonstrate experimentally that AlH(3) reacts with NaH to form NaAlH(4) without any requirement of a catalyst or hydrogen overpressure.

Recently CsTlCl 3 and CsTlF 3 perovskites were theoretically predicted to be potential superconductors if they are optimally doped. The synthesis of these two compounds, together with a complete characterization of the samples are reported. CsTlCl 3 is obtained as orange crystals in two different polymorphs: a tetragonal (I4/m) and a cubic (Fm-3m) phase. CsTlF 3 is formed as a light brown powder, also as a double cubic perovskite (Fm-3m). In all three CsTlX 3 phases Tl 1+ and Tl 3+ were located in two different crystallographic positions that accommodate their different bond lengths. In CsTlCl 3 some Tl vacancies are found in the Tl 1+ position. The charge ordering between Tl 1+ and Tl 3+ was confirmed by x-ray absorption and Raman spectroscopy. The Raman spectroscopy of CsTlCl 3 under high pressure (58 GPa) did not indicate any phase transition to a possible single Tl 2+ state. However, the highly insulating material becomes less resistive with increasing high pressure, while undergoing a change in the optical properties, from transparent to deeply opaque red, indicative of a decrease of the band gap. The theoretical design and experimental validation of the existence of CsTlF 3 and CsTlCl 3 cubic perovskites is the necessary first step in confirming the theoretical prediction of superconductivity in these materials.

A high-throughput method for measuring transition metal content based on quantitation of X-ray fluorescence signals was used to analyze 654 proteins selected as targets by the New York Structural GenomiX Research Consortium. Over 10% showed the presence of transition metal atoms in stoichiometric amounts; these totals as well as the abundance distribution are similar to those of the Protein Data Bank. Bioinformatics analysis of the identified metalloproteins in most cases supported the metalloprotein annotation; identification of the conserved metal binding motif was also shown to be useful in verifying structural models of the proteins. Metalloproteomics provides a rapid structural and functional annotation for these sequences and is shown to be approximately 95% accurate in predicting the presence or absence of stoichiometric metal content. The project's goal is to assay at least 1 member from each Pfam family; approximately 500 Pfam families have been characterized with respect to transition metal content so far.

Li 3 V 2 (PO 4 ) 3 /C (LVP/C) coated with various amounts of SiO 2 has been synthesized, and the effect of surface modification by SiO 2 on the performance of LVP has been systematically investigated with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), magnetic susceptibility, Raman spectroscopy, and electrochemical measurements. Based on the analysis of XRD, XPS, and TEM, it is confirmed that SiO 2 coating on the surface of LVP particles does not change the monoclinic structure of LVP. The XAS, XPS, and magnetic susceptibility results indicate that the valence of V in both the pristine and SiO 2 -coated LVP are close to +3. Furthermore, our results reveal that the electrochemical performance of LVP/ C can be significantly improved by the SiO 2 coating, which is due to the enhanced structural stability and reduced charge-transfer resistance.