Electronic structure study of hydrogen storage materials

First principles electronic structure studies can provide, at a microscopic level, an understanding of the, modification of the most fundamental properties of the matrix on hydrogen uptake such as metal-insulator transitions, magnetism, superconductivity, as well as a basic understanding of the hydrogen storage properties relevant to applications. To illustrating the latter point, we present an investigation of the properties of the hydrogen storage Ni-substituted LaNi5 intermetallic compounds. The effects of mono substitutions of Ni by 3d elements (Mn, Fe, Co), an s-p element of the 3d series, Cu, as well as by s-p elements of the IIIA (Al) and IVA series (Si, Ge, Sn) for several substitution rates are presented. We discuss the trends observed in the electronic structure and the factors that control : the stability of the intermetallic and their corresponding hydrides and the maximum hydrogen absorption capacity. We found that besides the elastic effects associated to volume changes on Ni substitutions, chemical bonding effects and band filling effects play a crucial role in controlling the storage properties of the materials. We also analyze the effect of polysubstitutions at the Ni site in LaNi3.5Al0.25Mn0.5Co0.75, a composition close to that of an industrial compound of good electrochemical performances, and we discuss the results in light of thermodynamic and spectroscopic data.