Improved hydrogen storage properties of MgH2 with Ni-based compounds

The nanoscaled Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) are synthesized by chemical methods. The MgH2-X (X = Ni3C, Ni3N, NiO and Ni2P) composites are prepared by mechanical ball-milling. The dehydrogenation properties of Mg-based composites are systematically studied using isothermal dehydrogenation apparatus, temperature-programmed desorption system and differential scanning calorimetry. It is experimentally confirmed that the dehydrogenation performance of the Mg-based materials ranks as following: MgH2Ni3C, MgH2Ni3N, MgH2NiO and MgH2Ni2P. The onset dehydrogenation temperatures of MgH2Ni3C, MgH2Ni3N, MgH2NiO and MgH2Ni2P are 160 °C, 180 °C, 205 °C and 248 °C, respectively. The four Mg-based composites respectively release 6.2, 4.9, 4.1 and 3.5 wt% H2 within 20 min at 300 °C. The activation energies of MgH2Ni3C, MgH2Ni3N, MgH2NiO and MgH2Ni2P are 97.8, 100.0, 119.7 and 132.5 kJ mol−1, respectively. It' found that the MgH2Ni3C composites exhibit the best hydrogen storage properties. Moreover, the catalytic mechanism of the Ni-based compounds is also discussed. It is found that Ni binding with low electron-negativity element is favorable for the dehydrogenation of the Mg-based composites.