Hydrogen dynamics in complex hydrides comprise long-range translational diffusion as well as localized motions like vibrations, librations, or rotations. All different motions are characterized by their specific length scale and time scales. Here we present a combined experimental and theoretical study on the rotational diffusion of the (BH4)− ions in crystalline NaBH4. The motion is thermally activated and characterized by an activation energy of 117 meV and a prefactor of 11 fs. Thereby the motion is dominated by 90° reorientations of the (BH4)− ion around the 4-fold symmetry axis of the cubic crystal. The experimental results are discussed on the basis of DFT calculations, revealing the potential energy landscape of a (BH4)− subunit in the crystalline matrix.

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.

We studied the decomposition reaction kinetics of lithium borohydride (LiBH4) with and without boron as an additive under various hydrogen pressures. The decomposition of LiBH4+B was studied by means of differential scanning calorimetry and thermogravimetry. Boron addition improves the dehydrogenation process, resulting in a decomposition temperature of 150 °C. A novel model was applied to separate thermodynamic and kinetic effects and to evaluate the activation energy of decomposition. The model takes into account the effect of hydrogen pressure on the reaction and allows us to evaluate the thermodynamic parameters, i.e., the enthalpy and entropy of reaction. Moreover, the effect of boron on the reaction kinetics is also demonstrated by the reduction of the activation energy from E a * = 59 ± 2 kJ/mol (pure system) to E a * = 54.8 ± 0.7 kJ/mol.