Lamellar high-entropy TiVCrMoC3 MXene enabling excellent hydrogen storage kinetics and cyclic stability of MgH2 via multi-phase interfaces and multiple transition metals effects

Abstract

MgH2 is a promising hydrogen storage medium, but its industrial use is hindered by high dehydrogenation temperatures and sluggish kinetics. Herein, a lamellar high-entropy TiVCrMoC3 MXene was synthesized via HF-mediated etching of a TiVCrMoAlC3 MAX precursor and integrated into MgH2 via high-energy ball-milling. The MgH2 + 7.5 wt. % TiVCrMoC3 composite exhibits a low-onset dehydrogenation temperature of 195 °C and releases 6.46 wt. % H2 within 10 min at 300 °C. The apparent activation energy drops from 140 to 90 kJ mol−1. For rehydrogenation, the fully dehydrogenated composite can initiate hydrogen absorption at room temperature (under 6 MPa) and uptakes 5.82 wt. % H2 within 60 min at 150 °C. Remarkably, it retains 99% of its initial capacity after 50 cycles. Microstructural investigation reveals that the unique lamellar morphology and multiple transition metal species of the TiVCrMoC3 MXene suppress the MgH2 grain agglomeration and establish multi-phase interfaces that facilitate hydrogen diffusion. Furthermore, density functional theory calculations demonstrate that the Mg–H bonds in Mg2H4 clusters adsorbed on the TiVCrMoC3 surface are significantly weakened due to prominent electron transfer channels between the clusters and transition metals. This work provides a novel strategy for regulating the hydrogen storage of MgH2 by high-entropy MXenes.