Metallic gallium: A liquid phase to destabilize nanoconfined LiBH4

Abstract

We present the effects of a gallium liquid phase over the hydrogen storage properties of LiBH4 nanoconfined in mesoporous carbon. This matrix was decorated with gallium by manual grinding. Nitrogen isotherms exposed the limited impact of grinding Ga over the micro/meso-porosity of the matrix. Electron microscopy showed deformed gallium nanodroplets, wetting and capped with carbon, ranging from micrometers to nanometers. Transmission electron microscopy established the presence of carbon shells covering nanodroplets of Ga. Powder X-ray diffractometry suggested the presence of liquid Ga, confirmed by differential scan calorimetry, with the observation at low temperatures of - and -phase gallium freezing/melting peaks. Gallium-decorated matrixes were melt-infiltrated with LiBH4. Nitrogen isotherms indicated that Ga nanodroplets had limited influence over the pore filling of the matrix by LiBH4. Despite carbon coverage, calorimetry established that Ga reduced the decomposition temperature of the hydride by at least 25 ºC at any filling values. It also demonstrated the interaction between the hydride and the metal, with peak broadening for each species and the disappearance of LiBH4´s melting peak. Initially, Ga decorating the matrix showed little influence over volumetric studies, but cooling the sample in liquid nitrogen reduced the hydride´s decomposition temperature by up to 17 ºC.