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

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 H-2 and 99.8 +/- 5.2 J K-1 per mole of H-2, 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 degrees 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.