Electrical energy storage for transportation has gone beyond the limit of converntional lithium ion batteries currently. New material or new battery system development is an alternative approach to achieve the goal of new high-energy storage system with energy densities 5 times or more greater. A series of SeSx-carbon (x = 0-7) composite materials has been prepared and evaluated as the positive electrodes in secondary lithium cells with ether-based electrolyte. In situ synchrotron high-energy X-ray diffraction was utilized to investigate the crystalline phase transition during cell cycling. Complementary, in situ Se K-edge X-ray absorption near edge structure analysis was used to track the evolution of the Se valence state for both crystalline and noncrystalline phases, including amorphous and electrolyte-dissolved phases in the (de)lithiation process. On the basis of these results, a mechanism for the (de)lithiation process is proposed, where Se is reduced to the polyselenides, Li2Sen (n ≥ 4), Li2Se2, and Li2Se sequentially during the lithiation and Li2Se is oxidized to Se through Li2Sen (n ≥ 4) during the delithiation. In addition, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy demonstrated the reversibility of the Li/Se system in ether-based electrolyte and the presence of side products in the carbonate-based electrolytes. For Li/SeS2 and Li/SeS7 cells, Li2Se and Li2S are the discharged products with the presence of Se only as the crystalline phase in the end of charge.

X-ray absorption fine structure (XAFS) spectroscopy was used to probe the effects of concentration on the first-shell structure of Ca2+ in aqueous solution. Measurements were carried out under ambient conditions using a bending magnet beamline (sector 20) at the Advanced Photon Source, Argonne. The Ca K-edge EXAFS spectrum for 6 m CaCl2 yielded no evidence for the formation of significant numbers of Ca2+−Cl- contact ion pairs even at such high concentration, a result confirmed by comparison with the data for a dilute (0.2 m) reference solution of the perchlorate. A mean coordination number of 7.2 ± 1.2 water molecules and an average Ca−O distance of 2.437 ± 0.010 Å were determined for 6 m CaCl2, and these parameters are also consistent with earlier EXAFS measurements on dilute Ca2+ solutions. Comparison of the pre-edge and near-edge (XANES) spectrum against those for various references, including the crystalline hydrates, provided further confirmation of the lack of change in the Ca2+ first-shell structure and symmetry. Our measurements help clarify the earlier results of modeling thermodynamic data that imply that some significant structural change occurs at high salt concentration. Taken together, our results suggest the formation of Ca2+−OH2−Cl- solvent-shared ion pairs, rather than Ca2+−Cl- contact ion pairs, is most likely responsible for the unusual thermodynamic behavior of this system. The EXAFS spectrum for an even more concentrated (9.2 m CaCl2) hexahydrate melt, however, did indicate the presence of some contact ion pairs. The new results agree closely with those of an earlier X-ray diffraction study, and serve to further aid interpretation of the aqueous solutions data. On a technical note, a previously unreported multielectron excitation edge at k = 10.2 Å-1 was detected in the EXAFS spectra and assigned to the KL II , III transition. Inclusion of this new transition, along with the other known (KM II , III and KM I ) transitions, in the background correction procedure significantly improved the quality of EXAFS fits. Further improvements resulted from the inclusion of Ca−H single scattering paths to treat the protons on the tightly bound water molecules. A Ca−H distance of 2.97 Å was obtained, which is in excellent agreement with the results of neutron scattering measurements (reported in part II). This appears to be the most convincing evidence to date for the detection of proton backscattering in EXAFS measurements of the local structure around ions in aqueous solution.

Higher animals typically rely on calcification to harden certain tissues such as bones and teeth. Some notable exceptions can be found in invertebrates: The fangs, teeth, and mandibles of diverse arthropod species have been reported to contain high levels of zinc. Considerable quantities of zinc also occur in the jaws of the marine polychaete worm Nereis sp. High copper levels in the polychaete worm Glycera dibranchiata recently were attributed to a copper-based biomineral reinforcing the jaws. In the present article, we attempt to unravel the role of zinc in Nereis limbata jaws, using a combination of position-resolved state-of-the-art techniques. It is shown that the local hardness and stiffness of the jaws correlate with the local zinc concentration, pointing toward a structural role for zinc. Zinc always is detected in tight correlation with chlorine, suggesting the presence of a zinc-chlorine compound. No crystalline inorganic phase was found, however, and results from x-ray absorption spectroscopy further exclude the presence of simple inorganic zinc-chlorine compounds in amorphous form. The correlation of local histidine levels in the protein matrix and zinc concentration leads us to hypothesize a direct coordination of zinc and chlorine to the protein. A comparison of the role of the transition metals zinc and copper in the jaws of two polychaete worm species Nereis and Glycera, respectively, is presented.

The subsurface behaviour of 99 Tc, a contaminant resulting from nuclear fuels reprocessing, is dependent on its valence (e.g., IV or VII). Abiotic reduction of soluble Tc(VII) by Fe(II) (aq) in pH 6-8 solutions was investigated under strictly anoxic conditions using an oxygen trap (<7.5 · 10 À9 atm O 2 ). The reduction kinetics were strongly pH dependent. Complete and rapid reduction of Tc(VII) to a precipitated Fe/Tc(IV) form was observed when 11 lmol/L of Tc(VII) was reacted with 0.4 mmol/L Fe(II) at pH 7.0 and 8.0, while no significant reduction was observed over 1 month at pH 6.0. Experiments conducted at pH 7.0 with Fe(II) (aq) = 0.05-0.8 mmol/L further revealed that Tc(VII) reduction was a combination of homogeneous and heterogeneous reaction. Heterogeneous reduction predominated after approximately 0.01 mmol/L of Fe(II) was oxidized. The heterogeneous reaction was more rapid, and was catalyzed by Fe(II) that adsorbed to the Fe/Tc(IV) redox product. Wet chemical and Fe-X-ray absorption near edge spectroscopy measurements (XANES) showed that Fe(II) and Fe(III) were present in the Fe/Tc(IV) redox products after reaction termination. 57 Fe-Mö ssbauer, extended X-ray adsorption fine structure (EXAFS), and transmission electron microscopy (TEM) measurements revealed that the Fe/Tc(IV) solid phase was poorly ordered and dominated by Fe(II)-containing ferrihydrite with minor magnetite. Tc(IV) exhibited homogeneous spatial distribution within the precipitates. According to Tc-EXAFS measurements and structural modeling, its molecular environment was consistent with an octahedral Tc(IV) dimer bound in bidentate edge-sharing mode to octahedral Fe(III) associated with surface or vacancy sites in ferrihydrite. The precipitate maintained Tc(IV) aq concentrations that were slightly below those in equilibrium with amorphous Tc(IV)O 2 AEnH 2 O (s) . The oxidation rate of sorbed Tc(IV) in the Fe/Tc precipitate was considerably slower than Tc(IV)O 2 AEnH 2 O (s) as a result of its intraparticle/intragrain residence. Precipitates of this nature may form in anoxic sediments or groundwaters, and the intraparticle residence of sorbed/precipitated Tc(IV) may limit 99 Tc remobilization upon the return of oxidizing conditions.