Study of new materials and their functionality for hydrogen storage and other energy applications

The first part of this thesis deals with hydrogen storage materials, in view of their applications as promising energy carriers. One of the main open problems with these materials is: how can their decomposition temperature be lowered, when hydrogen is wanted to be released, so as to improve the energy efficiency of the process. A possible answer is given by joint decomposition of two or more hydrides, if very stable mixed compounds are formed (‘hydride destabilization’). Aiming at this result, the new hydride composite 2LiBH4-Mg2FeH6 was considered, it was synthesized, and its thermodynamic and kinetic properties were investigated. In the second part of this thesis work lithium oxide materials, of relevant interest for applications to batteries, were investigated. The chemical lithiation reaction of niobium oxide was considered, as equivalent to the electrochemical process of lithium insertion on discharging a Nb2O5 cathode vs. a metal Li anode. Thus, the Li2Nb2O5 compound was synthesized by reaction of monoclinic a-Nb2O5 with n-butyllithium.This material was investigated by neutron powder diffraction (D2B equipment at ILL, France) and its structure was Rietveld refined in space group P2 to wRp=0.045, locating the Li atoms inserted in the a-Nb2O5 framework.