Bimetal Three-Dimensional MXene Nanostructures Stabilizing Magnesium Hydrides Realize Long Cyclic Life and Faster Kinetic Rates

Magnesium hydride (MgH₂) has attracted significant attention as a promising hydrogen storage material due to its large theoretical capacity (7.6 wt %); however, it suffers from high dehydrogenation temperature and poor kinetic rates, which limit its potential applications. Herein, we introduce a strategy for designing the three-dimensional (3D) dual transition metal MXene to tackle these problems simultaneously. The as-synthesized MgH₂@3D-TiVCT_x nanocomposite revealed that the dehydrogenation onset temperature reduced to 170 °C. This composite absorbed hydrogen about 6.5 wt % at 100 °C and released 5.5 wt % at 300 °C within 3 min. Furthermore, this composite achieved a long cyclic performance of 180 cycles at 250 °C with a negligible capacity decrease from 6.5 to 6.3 wt %. Structural analysis after the hydrogenation process and high capacity retention confirmed the stability and robustness of the 3D-TiVCT_x MXene structure. These remarkable results were attributed to the unique 3D-TiVCT_x MXene structure and in situ-formed Ti/V nanocatalysts, which not only stabilized the MgH₂ nanocrystallines but also provided multiphasic regions and heterojunctions that enhanced hydrogen growth and the recombination mechanism. The designing strategy for synthesizing a bimetallic 3D MXene structure offers valuable insights and opens significant possibilities for tailoring the hydrogen storage performance of MgH₂.