Graphene decorated with Fe nanoclusters for improving the hydrogen sorption kinetics of MgH2 – experimental and theoretical evidence

Abstract

Graphene decorated with Fe clusters is proposed to be a possible alternative catalyst for the hydrogenation and dehydrogenation reactions of MgH₂. In particular, graphene decorated with Fe clusters is effective for both hydrogenation and dehydrogenation processes of MgH₂. The change in enthalpy and entropy values of hydrogen absorption determined for MgH₂ with 5 wt% graphene decorated with Fe clusters is −50.4 ± 2.9 kJ per mole of H₂ and 99.8 ± 5.2 J K⁻¹ per mole of H₂, respectively. This is significantly lower than those for well-established metal catalysts and nano-interfacial confined MgH₂. Moreover, the graphene decorated with Fe clusters facilitates the fast rehydrogenation kinetics of MgH₂, which reabsorbed 90% of the total reabsorption capacity in less than 4 minutes at 300 °C and 20 atm. In addition, TEM analysis reveals that MgH₂ particles are covered by graphene with Fe clusters, resulting in the reduction of grain growth. Density functional theory shows that the defects in graphene act as the active sites for the dehydrogenation of MgH₂, while the Fe clusters reduce the adsorption of dissociated H atoms, resulting in low-temperature dehydrogenation. Thus, graphene decorated with metal clusters could open up a new way of designing a new type of catalyst which could replace transition metal catalysts.