Abstract
MgH2 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 TiVNbMoC3 high-entropy MXene derived from the TiVNbMoAlC3 MAX phase. This MXene was subsequently employed as an additive into MgH2 through ball milling treatment. For the MgH2 + 10 wt% TiVNbMoC3 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 H2 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 TiVNbMoC3 MXene can serves as a separator for preventing the MgH2 grain growth, while the Mg/MgH2/TiVNbMoC3 multiple-phase interfaces can also provide good channels for hydrogen adsorption, dissociation, and diffusion. Theoretical calculations suggest that the TiVNbMoC3 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 MgH2, 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 MgH2. This study offers a novel effective strategy for improving the hydrogen storage properties of MgH2 by high-entropy MXenes.