Synergistic effects of TiH2 and Pd on hydrogen desorption performances of MgH2

Abstract

In the present work, co-additives of Pd and TiH2 synergistically enhance the dehydrogenation performance of MgH2. The volumetric release measurements on 2MgH2–TiH2–0.1Pd composite revealed that the onset temperature of the dehydrogenation (150 °C) was greatly lowered by 150 °C from that of pristine MgH2. X-ray diffraction (XRD) analyses and high-resolution transmission electron microscopy (HR-TEM) observations found that Pd decomposed the MgH2 through yielding the Mg6Pd phase. The destabilizations of MgH2 in 2MgH2–0.1Pd and 2MgH2–TiH2–0.1Pd were confirmed by calculating the slopes of Van't Hoff plots of those composites based on pressure–composition isotherms. Those composites contain two significant plateaus in P–C isotherms of dehydrogenation, one represents the 2MgH2–0.1Pd release in initial stage, the other belongs to the self-decomposition of MgH2. TiH2 did not involve in the destabilization of MgH2 in the composite. However, it remarkably reduced the activation energy of the ternary system in dehydrogenation and improved its kinetics along with Pd. The activation energy value (77 kJ mol−1) of 2MgH2–TiH2–0.1Pd was found drastically lower than those of 2MgH2–0.1Pd (254.6 kJ mol−1) and 2MgH2–TiH2 (154.2 kJ mol−1). It exhibits that the synergistic effect by co-additives of TiH2 and Pd on dehydrogenation kinetics are more remarkable than any individual one.