High-entropy TiVNbMoC3 MXene as a highly efficient catalyst for improving the hydrogen storage properties of MgH2

MgH 2 is widely regarded as a promising solid-state hydrogen carrier. Nevertheless, the slow sorption rates and high thermal stability limit its commercial viability. To address these issues, this work describes the synthesis of a layered TiVNbMoC 3 high-entropy MXene derived from the TiVNbMoAlC 3 MAX phase. This MXene was subsequently employed as an additive into MgH 2 through ball milling treatment. For the MgH 2 + 10 wt% TiVNbMoC 3 composite, the initial temperature for hydrogen release is 190 °C, with 6.4 wt% of hydrogen liberated in 10 min at 300 °C. The dehydrogenation activation energy dropped from 145 to 92 kJ mol −1 . The dehydrogenated composite can start rehydrogenation at room temperature and has a hydrogen uptake capacity of 6.0 wt% within 60 min under conditions of 6 MPa H 2 and 150 °C. Furthermore, the sample exhibits excellent cycling stability, retaining 97% of its capacity after 50 cycles, with the hydrogen desorption amount slightly changing from 6.6 wt% in the second cycle to 6.4 wt% in the 50th cycle. Microstructural studies indicate that the layered TiVNbMoC 3 MXene can serves as a separator for preventing the MgH 2 grain growth, while the Mg/MgH 2 /TiVNbMoC 3 multiple-phase interfaces can also provide good channels for hydrogen adsorption, dissociation, and diffusion. Theoretical calculations suggest that the TiVNbMoC 3 MXene significantly weakens the Mg–H bond and an electron transfer channel is formed between the H atoms and the four transition metal atoms of high-entropy MXene. It is also believed that the high-entropy MXene can provide a large number of hydrogen adsorption sites for MgH 2 , which is helpful in capturing hydrogen atoms at the contact interface. The synergy of the above factors leads to the significant improvement of the hydrogen storage properties of MgH 2 . This study offers a novel effective strategy for improving the hydrogen storage properties of MgH 2 by high-entropy MXenes.