Improved dehydrogenation kinetics of MgH2 due to NiMnAl

Mg based nanocomposites containing different concentrations of NiMnAl alloy is studied in present work. Doped alloy was prepared by arc melting and ball milled to get its nano structure. Structural and hydrogen desorption properties of the composites were examined by x-ray diffraction(XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy and energy dispersive x-ray analysis (EDX). TGA study showed higher desorption temperature for as-milled MgH2 compared to MgH2-x wt% NiMnAl. Activation energy for hydrogen desorption was found to be -177.90, -173.09, -117.62 and -58.62 kJ mol(-1) for as-milled MgH2 and MgH2-x wt.% NiMnAl (x = 10, 25, 50) composites. In case of 50 wt% alloy additives the reduction of activation energy is 119.24 kJ mol(-1) resulting in improved hydrogen storage. XRD studies for phase and purity of as-milled MgH2 revealed that maximum stable and improved phase alteration for Hydrogen sorption was obtained for 25 wt% alloy. Morphology by SEM were undertaken to investigate the effect of hydrogenation of nanostructured alloy. DSC studies shows that increasing the concentration of NiMnAl in MgH2 from 25 to 50 wt% the onset temperature of hydrogen absorption decreased to about 40 degrees C.