Superior Catalytic Effect of Nickel Ferrite Nanoparticles in Improving Hydrogen Storage Properties of MgH 2

The catalysis of NiFe 2 O 4 nanoparticles on the hydrogen storage performances of magnesium hydride synthesized by high-energy ball milling was studied for the first time. The H 2 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 % NiFe 2 O 4 -doped MgH 2 is 191 °C, which is 250 °C lower than that of pristine MgH 2 . The desorption kinetics displays that the MgH 2 +7 mol % NiFe 2 O 4 sample could desorb 3.79 wt % H 2 within 1 h at 300 °C under H 2 pressure of 0.1 MPa. The absorption kinetics displays that the MgH 2 +7 mol % NiFe 2 O 4 sample could absorb 2.06 wt % H 2 within 3 h near room temperature under H 2 pressure of 4 MPa. The desorption activation energy of the MgH 2 +7 mol % NiFe 2 O 4 sample is 59.6 kJ/mol, decreasing 195.3 kJ/mol as compared with pristine magnesium hydride. The reaction enthalpy and entropy of the MgH 2 +7 mol % NiFe 2 O 4 sample during the dehydrogenation process are improved. The enhancement in the H 2 storage performances of MgH 2 by adding NiFe 2 O 4 nanoparticles is primarily ascribed to intermetallic Fe 7 Ni 3 and (Fe,Ni) phases during the desorption procedure, which act as the real catalyzer in the 7 mol % NiFe 2 O 4 -doped sample.