Superior effect of Ni-substitution on the hydrogenation kinetics of Mg6Pd1−xTMx (TM = Ag, Cu, Ni) pseudo-binary compounds

Abstract

In this investigation, the H-sorption kinetics of Mg6Pd and Mg6Pd1−xTMx (TM=Ag, Cu, Ni) pseudo-binary compounds at the TM solubility limit have been studied by isothermal hydrogen absorption, thermal desorption spectroscopy and in situ neutron diffraction. Among all studied compounds, the fastest absorption kinetics takes place for the Ni-substituted one. The fit of the absorption curves to established model equations for solid–gas reaction shows that hydrogenation is controlled by diffusion. As for desorption, the peak temperature for the Ni-substituted compound is 90K below that of MgH2/Mg system and is characterised by a low activation energy of 68kJ/molH2. To better understand these results, neutron diffraction experiments during in␣situ thermal desorption of deuterated Mg6Pd and Mg6Pd0.25Ni0.75 compounds were carried out. These experiments demonstrate a synergetic effect between MgH2 and Mg2NiH4 hydrides as responsible for the remarkable kinetics of the Ni-containing compound.