Fe3O4@graphene as a superior catalyst for hydrogen de/absorption from/in MgH2/Mg

The present investigation describes the hydrogen sorption (de/absorption) behavior of MgH2 catalyzed by graphene sheet templated Fe3O4 nanoparticles (Fe3O4@GS). Hydrogen sorption studies reveal that MgH2 catalyzed by Fe3O4@GS (MgH2:Fe3O4@GS) offers improved hydrogen storage behavior as compared to stand-alone MgH2 catalyzed by graphene sheets (GS) (MgH2: GS) or Fe3O4 nanoparticles (MgH2:Fe3O4). The MgH2:Fe3O4@GS has an onset desorption temperature of similar to 262 degrees C (similar to 142 degrees C lower than pristine MgH2), while MgH2:GS and MgH2:Fe3O4 have onset desorption temperatures of similar to 275 degrees C and similar to 298 degrees C respectively. In contrast to this, MgH2: GS absorbs 4.40 wt% and MgH2: Fe3O4 absorbs 5.50 wt% in 2.50 minutes at 290 degrees C under 15 atm hydrogen pressure. On the other hand, MgH2: Fe3O4@GS absorbs 6.20 wt% hydrogen in 2.50 minutes (which is considerably higher than recently studied catalyzed MgH2 systems) under identical temperature and pressure conditions. The MgH2 catalyzed with Fe3O4@GS shows negligible degradation of the storage capacity even after 25 cycles. Additionally, the desorption activation energy for MgH2: Fe3O4@GS has been found to be 90.53 kJ mol(-1) (which is considerably lower as compared to metal/metal oxide catalyzed MgH2 and fluorographene catalyzed MgH2). The formation enthalpy for MgH2:Fe3O4@GS is 60.62 kJ per mole of H-2 (13.44 kJ mol(-1) lower than bulk MgH2). The catalytic effect of Fe3O4@GS has been described and discussed with the help of structural (X-ray diffraction (XRD)), micro structural (electron microscopy) and Raman spectroscopic studies.