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

Abstract

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 °C. Furthermore, the onset temperatures of hydrogenation and dehydrogenation were significantly (i.e., 102 °C and 122 °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 °C with 5 wt% of the Y₂O₃@rGO composite. The values of 162.6 kJ mol⁻¹ H₂ and 145.9 kJ mol⁻¹ H₂ 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 H₂ and 54.3 kJ mol⁻¹ H₂ 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.