Enhanced low temperature hydrogen desorption properties and mechanism of Mg(BH4)2 composited with 2D MXene

Abstract

Mg(BH4)2 occupies a large hydrogen storage capacity of 14.7 wt%, and has been widely recognized to be one of the potential candidates for hydrogen storage. In this work, 2D MXene Ti3C2 was introduced into Mg(BH4)2 by a facile ball-milling method in order to improve its dehydrogenation properties. After milling with Ti3C2, Mg(BH4)2–Ti3C2 composites exhibit a novel “layered cake” structure. Mg(BH4)2 with greatly reduced particle sizes are found to disperse uniformly on Ti3C2 layered structure. The initial dehydrogenation temperature of Mg(BH4)2 has been decreased to 124.6 °C with Ti3C2 additive and the hydrogen liberation process can be fully accomplished below 400 °C. Besides, more than 10.8 wt% H2 is able to be liberated from Mg(BH4)2–40Ti3C2 composite at 330 °C within 15 min, while pristine Mg(BH4)2 merely releases 5.3 wt% hydrogen. Moreover, the improved dehydrogenation kinetics can be retained during the subsequent second and third cycles. Detailed investigations reveal that not only Ti3C2 keeps Mg(BH4)2 particles from aggregation during de/rehydrogenation, but also the metallic Ti formed in-situ serves as the active sites to catalyze the decomposition of Mg(BH4)2 by destabilizing the B–H covalent bonds. This synergistic effect of size reduction and catalysis actually contributes to the greatly advanced hydrogen storage characteristics of Mg(BH4)2.