Superior Catalytic Effect of Nickel Ferrite Nanoparticles in Improving Hydrogen Storage Properties of MgH2

The catalysis of NiFe2O4 nanoparticles on the hydrogen storage performances of magnesium hydride synthesized by high-energy ball milling was studied for the first time. The H2 storage performances and catalytic mechanism were studied by pressure–composition–temperature (PCT), differential scanning calorimetry (DSC), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The nonisothermal dehydrogenation results display that the initial dehydrogenation temperature of 7 mol % NiFe2O4-doped MgH2 is 191 °C, which is 250 °C lower than that of pristine MgH2. The desorption kinetics displays that the MgH2+7 mol % NiFe2O4 sample could desorb 3.79 wt % H2 within 1 h at 300 °C under H2 pressure of 0.1 MPa. The absorption kinetics displays that the MgH2+7 mol % NiFe2O4 sample could absorb 2.06 wt % H2 within 3 h near room temperature under H2 pressure of 4 MPa. The desorption activation energy of the MgH2+7 mol % NiFe2O4 sample is 59.6 kJ/mol, decreasing 195.3 kJ/mol as compared with pristine magnesium hydride. The reaction enthalpy and entropy of the MgH2+7 mol % NiFe2O4 sample during the dehydrogenation process are improved. The enhancement in the H2 storage performances of MgH2 by adding NiFe2O4 nanoparticles is primarily ascribed to intermetallic Fe7Ni3 and (Fe,Ni) phases during the desorption procedure, which act as the real catalyzer in the 7 mol % NiFe2O4-doped sample.