Cross-sectional TEM investigation of Mg-LaNi5-Soot hybrids for hydrogen storage

Abstract

Accumulatively roll bonded (ARB) Mg-LaNi5-Soot hybrid has emerged as a promising hydrogen storage material with enhanced hydrogen storage characteristics, which is amenable to scaled-up production. The key to understanding the hydrogen storage behaviour lies in the nanoscale structure of the hybrid and the associated mechanisms. The focus of the current study is on the use of cross-sectional transmission electron microscopy (TEM) to unravel the underlying mechanisms of hydrogen storage, in the Mg-LaNi5-Soot hybrid. The role of processing variables (ARB passes and strain) and the concomitant evolution of the microstructure (distribution of second phase particles (LaNi5 and soot)) are studied, keeping in view the diffusion of hydrogen and the nucleation of the hydride phase. It is established that the interface between Mg and second phase (LaNi5 and soot) plays a dominant role in the nucleation of the MgH2 phase. The MgH2 nucleation mechanism is studied under the ambit of the Johnson-Mehl-Avrami kinetic (JMAK) model. It is concluded that the internal interfaces provides sites for the nucleation of magnesium hydride.