2D transition metal carbides trigger enhanced dehydrogenation and reversibility properties in Mg(BH4)2

Abstract

Although Mg(BH4)2 has been widely studied in the hydrogen storage field for its high hydrogen density, its terrible dehydriding kinetics and cycling features remain impediments to practical applications. Herein, introducing different MXenes (Ti3C2, Ti2C, Nb2C) with novel two-dimensional structures as catalysts into Mg(BH4)2 has been demonstrated to be an efficient approach to boosting the hydrogen storage properties. 30 wt% MXenes in Mg(BH4)2 causes a considerable reduction in its hydrogen release temperature, remarkable increases in its dehydrogenation rate and capacity, and an enhancement to its reversibility. The Mg(BH4)2-30Ti2C as the most excellent composite starts to liberate hydrogen from 132 °C, 143 °C lower than that of Mg(BH4)2. Furthermore, at 260 °C, the Mg(BH4)2-30Ti2C composite desorbs 10.2 wt% H2, which is much higher than that of Mg(BH4)2 (1.5 wt%). Theoretical calculations elucidate the weakening of B-H bonds caused by the electron transfer at the Mg(BH4)2/MXenes interfaces, and the dehybridization effect between the B and H orbits. X-ray photoelectron spectroscopy (XPS) analyses prove the in-situ formation of multiphase interfaces resulting from the interaction of Mg(BH4)2 and MXenes during milling and dehydrogenation processes, which could increase electron conduction and facilitate hydrogen diffusion. These factors contribute to the outstanding dehydrogenation properties of Mg(BH4)2.