A way to circumvent the high pressures needed to metallize hydrogen is to “precompress” it in hydrogen-rich molecules, a strategy probed theoretically for silane. We show that phases with tetrahedral ${\mathrm{SiH}}_4$ molecules should undergo phase transitions with sixfold- and eightfold-coordinate Si appearing above 25 GPa. The most stable structure found can be metallized at under a megabar and at a compression close to the prediction of Goldhammer-Herzfeld criterion. According to a BCS-like estimate, metallic silane should be a high-temperature superconductor.

The widespread adoption of hydrogen as an energy carrier could bring significant benefits, but only if a number of currently intractable problems can be overcome. Not the least of these is the problem of storage, particularly when aimed at use onboard light-vehicles. The aim of this overview is to look in depth at a number of areas linked by the recently concluded HYDROGEN research network, representing an intentionally multi-faceted selection with the goal of advancing the field on a number of fronts simultaneously. For the general reader we provide a concise outline of the main approaches to storing hydrogen before moving on to detailed reviews of recent research in the solid chemical storage of hydrogen, and so provide an entry point for the interested reader on these diverse topics. The subjects covered include: the mechanisms of Ti catalysis in alanates; the kinetics of the borohydrides and the resulting limitations; novel transition metal catalysts for use with complex hydrides; less common borohydrides; protic-hydridic stores; metal ammines and novel approaches to nano-confined metal hydrides.

Significance: Antiferromagnets can host strong quantum fluctuations in their ground state if they combine both low dimensionality and low spin. Materials based on copper oxides (spin-1/2 ions in layered or 1D structures) are unique in optimizing the tendency to strong quantum fluctuations. As a bonus, they show extremely large magnetic interactions, which lead to interesting quantum effects at relatively high temperatures as anomalous transport properties and high- T c superconductivity in doped systems. Obtaining similar features with other ions has been a long-standing goal. We show that silver and fluorine (which are next to copper and oxygen in the periodic table) in the commercial compound A g F 2 reach the goal, paving the way for a different generation of quantum materials.

Fourteen different synthetic approaches towards pure solvent-free Y(BH₄)₃ have been tested, thirteen of which have failed. Attempted reactions of YCl₃ or Y(OC₄H₉)₃ with LiBH₄ in THF, those of YCl₃ with (C₄H₉)₄N⁺ BH₄ ⁻, as well as between YH_x∼3 and R₄NBH₃ (R = CH₃, C₂H₅) in the presence or absence of a solvent (n-hexane or CH₂Cl₂) did not lead to the expected product. The mechanochemical solid/solid reactions (MBH₄ + 3 YX₃→ Y(BH₄)₃ + 3 LiCl, where M = Li, Na; X = F, Cl) have succeeded only for the LiBH₄ and YCl₃ reagents, but the separation of the crystalline reaction products (Y(BH₄)₃ in its Pa phase and LiCl) by dissolution or flotation in various solvents has not been successful. The thermal decomposition process of Y(BH₄)₃ in a mixture with LiCl has been investigated with thermogravimetric (TGA) and calorimetric analysis (DSC) combined with spectroscopic evolved gas analysis (EGA). Three major endothermic steps could be distinguished in the DSC profile at ca. 232, 282, 475 °C (heating rate 10 K min⁻¹) corresponding to a phase transition and two steps of thermal decomposition. Solid decomposition products are amorphous except for the new cubic polymorph of Y(BH₄)₃ overlooked in previous work. The high-temperature phase forms at the onset of thermal decomposition and it may be prepared by heating of the low-temperature phase up to a narrow temperature range (194–210 °C) followed by rapid quenching. Y(BH₄)₃ constitutes a novel highly efficient hydrogen storage material (theor. 9.0 wt% H) but, unfortunately, the evolved H₂ is contaminated by toxic boron hydrides and products of their pyrolysis.