Multifunctional Mo4/3B2-x MBene for high hydrogen storage performance in the Li–Mg–N–H system

The magnesium-based hydrogen storage composite system Li–Mg–N–H (Mg(NH 2 ) 2 –2LiH) has attracted considerable attention due to its moderate operating temperature and high reversible capacity of 5.6 wt%, but its sluggish hydrogen absorption/desorption kinetics and poor cycling stability limit practical applications. Introducing an efficient catalyst is key to overcoming these issues. Herein, for the first time, an MBene material is introduced into a solid-state hydrogen storage system. Mo 4/3 B 2- x with a flower-like structure is successfully prepared by selective etching of the MAB phase (Mo 4/3 Y 2/3 AlB 2 ) and is then added as a catalyst into the Mg(NH 2 ) 2 –2LiH system. The improving effect and the underlying mechanism on hydrogen storage performance are systematically investigated. The results show that the composite with 10 wt% Mo 4/3 B 2- x exhibits optimal comprehensive performance. The onset temperatures for hydrogen absorption and desorption are significantly reduced from 110/130°C to 65/106°C, respectively. The hydrogen absorption/desorption capacities exceed 4.7 wt% under isothermal conditions at 180°C/170°C, and the apparent activation energy for hydrogen desorption decreases from 117.0 kJ/mol to 87.5 kJ/mol. Remarkably, after 100 cycles, the reversible capacity remains above 4.47 wt%, demonstrating excellent cycling stability. Mechanistic studies combined with DFT calculations reveal that the flower-like Mo 4/3 B 2- x dissociates into fine petals and becomes highly dispersed in the matrix during ball milling. The interaction between the catalyst and the matrix effectively weakens the N–H and Mg–N bonds and promotes the retention of the cubic phase Li 2 MgN 2 H 2 in the hydrogen desorption product, which is more favorable for rehydrogenation. Meanwhile, abundant boron vacancies in the catalyst structure provide fast diffusion channels for hydrogen atoms, and the highly dispersed nano-petals effectively separate the matrix particles, collectively enhancing the kinetics and cycling performance. This work opens a new direction for the application of MBene materials in solid-state hydrogen storage and provides a new strategy for the rational design of high-performance hydrogen storage catalysts.