Bimetallic Ti 2 NbC 2 MXene as an efficient catalyst for reversible hydrogen storage in magnesium hydride

Abstract Magnesium hydride (MgH 2 ) was highly regarded for its substantial hydrogen storage capacity of up to 7.6 wt%, but its commercial application was hindered by the high operating temperatures and slow kinetics. In this study, the successful synthesis of the layered Ti 2 NbC 2 has significantly enhanced the hydrogen storage performance of MgH 2 . MgH 2 + 5 wt% Ti 2 NbC 2 began to release hydrogen at 190 °C and started to absorb hydrogen at room temperature. At a constant temperature of 275 °C, complete hydrogen release was achieved in just 250 s, up to 6.9 wt%. At 150 °C, the absorption of hydrogen reached 6.59 wt% within 200 s, and the hydrogen absorption activation energy was reduced to 41.517 ± 3.981 kJ·mol −1 , significantly improving the kinetic performance. Moreover, the composite material still exhibited excellent cyclic stability after 20 cycles at 275 °C. In the process of hydrogen de/absorption of Ti 2 NbC 2 with MgH 2 , active substances Nb–H and Ti–H were generated in situ, which effectively weakened the Mg–H bond and acted as efficient “hydrogen pumps” to accelerate the re/dehydrogenation of MgH 2 . The unique layered structure and hydrogen affinity of Ti 2 NbC 2 provided an effective transfer channel for hydrogen migration, which was key to the excellent hydrogen storage performance of the MgH 2 + Ti 2 NbC 2 .