Metal hydrides are likely candidates for the solid state storage of hydrogen. NaAlH 4 is the only complex metal hydride identified so far that combines favorable thermodynamics with a reasonable hydrogen storage capacity (5.5 wt %) when decomposing in two steps to NaH, Al, and H 2 . The slow kinetics and poor reversibility of the hydrogen desorption can be combatted by the addition of a Ti-based catalyst. In an alternative approach we studied the influence of a reduced NaAlH 4 particle size and the presence of a carbon support. We focused on NaAlH 4 /porous carbon nanocomposites prepared by melt infiltration. The NaAlH 4 was confined in the mainly 2-3 nm pores of the carbon, resulting in a lack of long-range order in the NaAlH 4 structure. The hydrogen release profile was modified by contact with the carbon; even for ∼10 nm NaAlH 4 on a nonporous carbon material the decomposition of NaAlH 4 to NaH, Al, and H 2 now led to hydrogen release in a single step. This was a kinetic effect, with the temperature at which the hydrogen was released depending on the NaAlH 4 feature size. However, confinement in a nanoporous carbon material was essential to not only achieve low H 2 release temperatures, but also rehydrogenation at mild conditions (e.g., 24 bar H 2 at 150 °C). Not only had the kinetics of hydrogen sorption improved, but the thermodynamics had also changed. When hydrogenating at conditions at which Na 3 AlH 6 would be expected to be the stable phase (e.g., 40 bar H 2 at 160 °C), instead nanoconfined NaAlH 4 was formed, indicating a shift of the NaAlH 4 TNa 3 AlH 6 thermodynamic equilibrium in these nanocomposites compared to bulk materials.

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The predominant means to detect nuclear magnetic resonance (NMR) is to monitor the voltage induced in a radiofrequency coil by the precessing magnetization. To address the sensitivity of NMR for mass-limited samples it is worthwhile to miniaturize this detector coil. Although making smaller coils seems a trivial step, the challenges in the design of microcoil probeheads are to get the highest possible sensitivity while maintaining high resolution and keeping the versatility to apply all known NMR experiments. This means that the coils have to be optimized for a given sample geometry, circuit losses should be avoided, susceptibility broadening due to probe materials has to be minimized, and finally the B(1)-fields generated by the rf coils should be homogeneous over the sample volume. This contribution compares three designs that have been miniaturized for NMR detection: solenoid coils, flat helical coils, and the novel stripline and microslot designs. So far most emphasis in microcoil research was in liquid-state NMR. This contribution gives an overview of the state of the art of microcoil solid-state NMR by reviewing literature data and showing the latest results in the development of static and micro magic angle spinning (microMAS) solenoid-based probeheads. Besides their mass sensitivity, microcoils can also generate tremendously high rf fields which are very useful in various solid-state NMR experiments. The benefits of the stripline geometry for studying thin films are shown. This geometry also proves to be a superior solution for microfluidic NMR implementations in terms of sensitivity and resolution.

Quasiparticle tunneling measurements of the high-temperature superconductors HgBa 2 Ca nϪ1 Cu n O 2nϩ2ϩ␦ (Hg-12(nϪ1)n,nϭ1,2,3) are considered in the context of d x 2 Ϫy 2 symmetry of the superconducting order parameter and a two-dimensional ͑2D͒ van Hove singularity ͑vHs͒ related to saddle points in the electronic band structure. Normal-metal-insulator-superconductor tunneling spectra taken at 4.2 K with a scanning tunneling microscope on Hg-1212 c-axis epitaxial films, as well as on Hg-1201 and Hg-1223 polycrystalline samples, show distinct gap characteristics which cannot be easily reconciled with the simple s-wave BCS density of states. The data are analyzed with the nodal d-wave gap function ⌬ k ϭ⌬ 0 (cos k x Ϫcos k y )/2 and the 2D tight-binding electronic dispersion k ϭϪ2t(cos k x ϩcos k y )ϩ4tЈ(cos k x cos k y )Ϫ, using the quasiparticle tunneling formalism for elastic and specular transmission. The analysis indicates a highly directional and energy-dependent spectral weighting, related to the gap anisotropy and band-structure dependence of the tunneling matrix element ͉T͉ 2 , and successfully explains the observed gap spectra. Values for the d-wave gap maximum are determined to be ⌬ 0 Ϸ33, 50, and 75 meV, respectively, for optimally doped Hg-1201, Hg-1212, and Hg-1223, corresponding to reduced-gap ratios of 2⌬ 0 /k B T c Ϸ7.9, 9.5, and 13. These ratios are substantially larger than the BCS weak-coupling limit of 3.54. A comparison with data from other high-T c cuprates indicates an overall trend of 2⌬ 0 /k B T c rising with T c , in violation of BCS universality.

In the search for suitable solid state hydrogen storage systems, NaAlH 4 (7.4 wt % H 2 ) holds great promise due to its suitable thermodynamical properties. However, hydrogen release and uptake are hampered by high activation energies, most likely due to solid state mass transfer limitations. A recent strategy to improve the hydrogen de-and rehydrogenation properties of NaAlH 4 is to reduce the particle size to the nanometer scale. We prepared high loadings of nanosized NaAlH 4 confined in the pores of a carbon support by melt infiltration. XRD, nitrogen physisorption, high pressure DSC and solid-state NMR are used to evidence that the molten NaAlH 4 infiltrates the carbon support, and forms a nanosized NaAlH 4 phase lacking long-range order. The confined NaAlH 4 shows enhanced hydrogen dehydrogenation properties and rehydrogenation under mild conditions that is attributed to the nanosize and close contact to the carbon matrix.