Nanostructuring and catalyzing are effective methods for improving the hydrogen storage properties of MgH2. In this work, transition-metal-carbides (TiC, ZrC and WC) are introduced into Mg-Ni alloy to enhance its hydrogen storage performance. 5 wt% transition metal-carbide containing Mg95Ni5 (atomic ratio) nanocomposites are prepared by mechanical milling pretreatment followed by hydriding combustion synthesis and mechanical milling process, and the synergetic enhancement effects of Mg2NiH4 and transition metal-carbides are investigated systematically. Due to the inductive effect of Mg2NiH4 and charge transfer effect between Mg/MgH2 and transition-metal-carbides, Mg95Ni5-5 wt.% transition-metal-carbide samples all exhibit excellent hydrogen storage kinetic at moderate temperature and start to release hydrogen around 216 degrees C. Among them, 2.5 wt% H-2 (220 degrees C) and 4.7 wt% H-2 (250 degrees C) can be released from the Mg95Ni5-5 wt.% TiC sample within 1800 s. The unique mosaic structure endows the Mg95Ni5-5 wt.% TiC with excellent structural stability, thus can reach 95% of saturated hydrogen capacity within 120 s even after 10 cycles of de-/hydrogenation at 275 degrees C. And the probable synergistic enhancement mechanism for hydrogenation and dehydrogenation is proposed. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.