Catalytic action of Y2O3@graphene nanocomposites on the hydrogen-storage properties of Mg-Al alloys

An Y2O3@rGO nanocomposite was synthesized via an impregnation method and the catalytic effect of the nanocomposite on the hydrogen-storage properties of a Mg-Al alloy was investigated. The pressure composition isotherm measurement results revealed that the Mg-Al-Y2O3@rGO composite underwent a reversible hydrogenation/dehydrogenation process at 250 degrees C. Furthermore, the onset temperatures of hydrogenation and dehydrogenation were significantly (i.e., 102 degrees C and 122 degrees C, respectively) lower than the respective values corresponding to the Mg-Al alloy. The Y2O3@rGO nanocomposite enhanced the hydriding kinetic properties of the alloy. The hydrogenation kinetic parameter of the Mg-Al alloy increased from 0.008 to 0.195 at 300 degrees C with 5 wt% of the Y2O3@rGO composite. The values of 162.6 kJ mol(-1) H-2 and 145.9 kJ mol(-1) H-2 were obtained for the dehydrogenation energy barrier (evaluated by means of a Kissinger plot) of the Mg-Al alloy and the Mg-Al-Y2O3@rGO hydride, respectively. The reaction enthalpy of hydrogenation/dehydrogenation (determined from a van't Hoff plot) of the alloy decreased with the addition of the Y2O3@rGO nanocomposite. For example, the values of 70.7 kJ mol(-1) H-2 and 54.3 kJ mol(-1) H-2 were obtained for the reaction enthalpy of hydrogenation associated with the Mg-Al alloy and the Mg-Al-Y2O3@rGO composite, respectively. Therefore, the addition of the Y2O3@rGO nanocomposite is conducive for improving the thermodynamic and kinetic properties of hydrogenation/dehydrogenation of the Mg-Al alloy.