A novel solid-solution MXene (Ti0.5V0.5)3C2 with high catalytic activity for hydrogen storage in MgH2

A novel solid-solution MXene (Ti0.5V0.5)3C2 is successfully synthesized by exfoliating a solid-solution MAX phase (Ti0.5V0.5)3AlC2, and its catalytic effect on the hydrogen storage reaction of Mg is systemically evaluated for the first time. Typical layer morphology is observed for the prepared (Ti0.5V0.5)3C2, which exhibits a better catalytic activity than that of Ti3C2. The addition of 10 wt% (Ti0.5V0.5)3C2 remarkably reduces the dehydrogenation onset temperature of MgH2 by 70 °C, from 266 to 196 °C. At 250 °C, approximately 5.0 wt% H2 is released from the 10 wt% (Ti0.5V0.5)3C2-containing MgH2 within 20 min. The dehydrogenated sample rapidly absorbs 4.8 wt% H2 within 5 s at 120 °C; these hydrogenation kinetics are much more superior even to the well-studied Nb2O5 catalyst. The apparent activation energy is calculated to be 77.3 kJ/mol for the MgH2-10 wt% (Ti0.5V0.5)3C2 sample, which is only around half of that of the pristine MgH2 (153.8 kJ/mol). This is responsible for the remarkably reduced dehydrogenation operating temperature. Moreover, the chemical states of (Ti0.5V0.5)3C2 during dehydrogenation are also analysed and discussed.