Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid‐state batteries. LiBH4 is a promising solid electrolyte for Li‐ion batteries. It displays high lithium mobility, although only above 110 °C at which a transition to a high temperature hexagonal structure occurs. Herein, it is shown that confining LiBH4 in the pores of ordered mesoporous silica scaffolds leads to high Li+ conductivity (0.1 mS cm−1) at room temperature. This is a surprisingly high value, especially given that the nanocomposites comprise 42 vol% of SiO2. Solid state 7Li NMR confirmed that the high conductivity can be attributed to a very high Li+ mobility in the solid phase at room temperature. Confinement of LiBH4 in the pores leads also to a lower solid‐solid phase transition temperature than for bulk LiBH4. However, the high ionic mobility is associated with a fraction of the confined borohydride that shows no phase transition, and most likely located close to the interface with the SiO2 pore walls. These results point to a new strategy to design low‐temperature ion conducting solids for application in all solid‐state lithium ion batteries, which could enable safe use of Li‐metal anodes.

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.

NaBH 4 is an interesting hydrogen storage material for mobile applications due to its high hydrogen content of 10.8 wt%. However, its practical use is hampered by the high temperatures (above 500 C) required to release the hydrogen and by the non reversibility of the hydrogen sorption. In this study, we show that upon heating to 600 C, bulk NaBH 4 decomposed into Na and Na 2 B 12 H 12 , releasing the expected 8.1wt% of hydrogen. Nanosizing and confinement of NaBH 4 in porous carbon resulted in much faster hydrogen desorption kinetics. The onset of hydrogen release was reduced from 470 C for the bulk to below 250 C for the nanocomposites. Furthermore, the dehydrogenated nanocomposites were partially rehydrogenated to form NaBH 4 , with the absorption of about 43% of the initial hydrogen capacity at relatively mild conditions (60 bar H 2 and 325 C). Reversibility in this system was limited due to partial loss of Na during dehydrogenation. The dehydrogenated boron compounds were almost fully rehydrogenated to NaBH 4 (98%) when extra Na was added to the nanocomposites. To the best of our knowledge, this is the first time that reversibility for NaBH 4 has been demonstrated.

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.

The structural and dynamical properties of LiBH 4 confined in porous carbon and ordered porous silica are studied using Li measurements show that Li + is also highly mobile. Therefore, we conclude that nanoconfinement of LiBH 4 strongly enhances diffusional mobility of borohydride anions and lithium in this material.