Enhanced hydrogen sorption kinetics of MgH2 catalyzed by a novel layered Ni/Al2O3 hybrid

Abstract Metal-containing catalysts have been successfully applied in the Mg-based hydrogen storage materials. Here, a layered Ni/Al2O3 obtained by calcination of NiAl-layered double hydroxide (NiAl-LDH) is firstly reported for enhancing hydrogen sorption kinetics of MgH2. The hybrid catalyst of Ni/Al2O3 with high stability shows better catalytic performance than the corresponding complex oxides: the onset dehydrogenation temperature of MgH2-Ni/Al2O3 (190 °C) is much lower than that of MgH2-NiO/Al2O3 (240 °C) and the as-milled MgH2 (298 °C), and the MgH2-5 wt.% Ni/Al2O3 desorbs about 5.6 wt.% hydrogen within 3500 s at 275 °C, while only 4.6 wt.% hydrogen is released for MgH2-5 wt.% NiO/Al2O3 and the undoped MgH2 can hardly dehydrogenate at the same conditions. The catalytic mechanism of Ni/Al2O3 was investigated in detail by combining the experiment and density functional theory (DFT) calculations. The enhanced hydrogen desorption kinetics is mainly due to the destabilizing effect of MgH2 caused by Ni/Al2O3 acting as electron acceptors to capture the electrons in the Mg−H bond, resulting in a weakening of the bond strength. This study might be of interest for designing high-efficiency metal-metal oxide hybrid catalysts applied in the field of hydrogen storage.