Synergistic catalytic effects of ZIF-67 and transition metals (Ni, Cu, Pd, and Nb) on hydrogen storage properties of magnesium

Abstract

MgTM/ZIF-67 nanocomposites were prepared by the deposition-reduction method using ZIF-67, MgCl2, and TMClx (TM = Ni, Cu, Pd, Nb) as raw materials. The dehydrogenation activation energies of MgTM/ZIF-67 (TM = Ni, Cu, Pd, Nb) nanocomposites were calculated to be 115.4 kJ mol−1 H2, 115.7 kJ mol−1 H2, 113.6 kJ mol−1 H2, and 75.8 kJ mol−1 H2, respectively; hence, the MgNb/ZIF-67 nanocomposite manifested the best comprehensive hydrogen storage performance. The hydrogen storage capacity of the MgNb/ZIF-67 nanocomposite was hardly attenuated after the 100th hydrogen absorption-desorption cycle. The dehydrogenated enthalpies of MgH2 and CoMg2H5 in MgNb/ZIF-67 hydride were calculated to be 72.4 kJ mol−1 H2 and 81.0 kJ mol−1 H2, respectively, which were lower than those of additive-free MgH2 and Mg/ZIF-67. The improved hydrogen storage properties of MgNb/ZIF-67 can be ascribed to the CoMg2–Mg(Nb) core-shell structure and the catalytic effects of NbH and niobium oxide nanocrystals.