Structure of nanoconfined LiBH4 from first principles 11B NMR chemical shifts calculations

Abstract

Nanoconfinement of metal borohydrides is a promising route for improvement of their kinetic and thermodynamic properties related to hydrogen storage. Since the atomic-scale properties of nanoconfined LiBH4 remain under debate we propose a model of such a structure. Within extensive density functional theory calculations we consider continuous transformation of the lithium borohydride equilibrium structures from 3-dimensional to 1-dimensional. Such structures consist of single linear chains, linear ribbons and 3-dimensional chains, and together with the low temperature bulk phase they reproduce 11B NMR spectra observed in LiBH4 confined in porous carbon. The present model suggest that nanoconfined LiBH4 consists of a dense bulk-like region and loosely distributed chains and ribbons of Li–BH4. Even with the low effective density of loosely distributed LiBH4 they occupy region with thickness as small as a quarter of a pore diameter.