Julián Puszkiel

Structural and kinetic investigation of the hydride composite Ca(BH4)2 + MgH2 system doped with NbF5 for solid-state hydrogen storage

Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen-metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques.

KNH2–KH: a metal amide–hydride solid solution

We report for the first time the formation of a metal amide-hydride solid solution. The dissolution of KH into KNH2 leads to an anionic substitution, which decreases the interaction among NH2- ions. The rotational properties of the high temperature polymorphs of KNH2 are thereby retained down to room temperature.

A novel catalytic route for hydrogenation–dehydrogenation of 2LiH + MgB2via in situ formed core–shell LixTiO2 nanoparticles

Aiming to improve the hydrogen storage properties of 2LiH + MgB2 (Li-RHC), the effect of TiO2 addition to Li-RHC is investigated. The presence of TiO2 leads to the in situ formation of core–shell LixTiO2 nanoparticles during milling and upon heating. These nanoparticles markedly enhance the hydrogen storage properties of Li-RHC. Throughout hydrogenation–dehydrogenation cycling at 400 °C a 1 mol% TiO2 doped Li-RHC material shows sustainable hydrogen capacity of ∼10 wt% and short hydrogenation and dehydrogenation times of just 25 and 50 minutes, respectively. The in situ formed core–shell LixTiO2 nanoparticles confer proper microstructural refinement to the Li-RHC, thus preventing the materials agglomeration upon cycling. An analysis of the kinetic mechanisms shows that the presence of the core–shell LixTiO2 nanoparticles accelerates the one-dimensional interface-controlled mechanism during hydrogenation owing to the high Li+ mobility through the LixTiO2 lattice. Upon dehydrogenation, the in situ formed core–shell LixTiO2 nanoparticles do not modify the dehydrogenation thermodynamic properties of the Li-RHC itself. A new approach by the combination of two kinetic models evidences that the activation energy of both MgH2 decomposition and MgB2 formation is reduced. These improvements are due to a novel catalytic mechanism via Li+ source/sink reversible reactions.