Excellent synergistic catalytic mechanism of in-situ formed nanosized Mg2Ni and multiple valence titanium for improved hydrogen desorption properties of magnesium hydride.

Abstract Nowadays, catalytic doping has been regarded as one of the most promising and effective methods to improve the sluggish kinetics of magnesium hydride (MgH 2). Herein, we synthesized Ni/TiO 2 nanocomposite with the particle sizes about 20 nm by an extremely facile solvothermal method. Then, the Ni/TiO 2 nanocomposite was doped into MgH 2 to enhance its reversible hydrogen storage properties. A remarkably enhancement of de/rehydrogenation kinetics of MgH 2 can be achieved by doped with Ni/TiO 2 nanocomposite, compared to that solely doped with Ni or TiO 2 nanoparticles. The hydrogen desorption peak temperature of MgH 2 Ni/TiO 2 is 232 °C, which is 135.4 °C lower than that of ball-milled MgH 2 (367.4 °C). Moreover, the MgH 2 Ni/TiO 2 can desorb 6.5 wt% H 2 within 7 min at 265 °C and absorb ∼5 wt% H 2 within 10 min at 100 °C. In particular, the apparent activation energy of MgH 2 Ni/TiO 2 is obviously decreased from 160.5 kJ/mol (ball-milled MgH 2) to 43.7 ± 1.5 kJ/mol. Based on the analyses of microstructure evolution, it is proved that metallic Ni particles can react with Mg easily to form fine Mg 2 Ni particles after dehydrogenation, and the in-situ formed Mg 2 Ni will transform into Mg 2 NiH 4 in the subsequent rehydrogenation process. The significantly improved hydrogen absorption/desorption properties of MgH 2 Ni/TiO 2 can be ascribed to the synergistic catalytic effect of reversible transformation of Mg 2 Ni/Mg 2 NiH 4 which act as "hydrogen pump", and the multiple valence titanium compounds (Ti4+/3+/2+) which promote the electrons transfer of MgH 2 /Mg. Highlights • Ni/TiO 2 with particle sizes ∼20 nm was synthesized and doped into MgH 2. • MgH 2 Ni/TiO 2 starts to release hydrogen at 190 °C with ∼6.5 wt% H 2. • Enhanced hydrogen storage properties are due to synergistic catalytic mechanism. [ABSTRACT FROM AUTHOR]