Chemico-physical characterization and hydrogen sorption properties of chemical hydrides confined into mesoporous scaffolds

Within the widespread activity in the development of innovative hydrogen storage materials, rising attention has been recently addressed to the sorption properties of nanosized materials confined into the mesoporous networks of matrixes with different chemical nature. Improvements of the thermodynamic properties and kinetics of hydrogen release and uptake are expected through the reduction to nanometer scale and the control of grain size of hydrides particles. As a further beneficial effect, the undesired grain growth and particle agglomeration would be avoided. In this work, the possibility to infiltrate single and multicomponent chemical hydrides into Si- and C- matrices is explored. In particular, NaBH4 and NaBH4 - MgH2 mixtures were embedded in Si-based and C-based high surface matrixes and LiBH4-MgH2 mixtures in C aerogel matrices by wet chemical impregnation and melting infiltration. Structural characterization was performed by X-Ray diffraction, small angle neutron scattering and transmission electron microscopy in order to estimate the efficiency of impregnation techniques. The thermodynamics and kinetics of the absorption and desorption processes and the chemical nature of the released gas were analyzed by high-pressure calorimetry, manometric measurements and mass spectroscopy. A noticeable reduction in the temperature of the sorption steps, in the desorption enthalpies and in the activation energies with respect to the mixtures in powder form is evident for both the explored systems. Full reversibility of the sorption processes has been demonstrated for the Li-containing system.