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

Abstract A novel solid-solution MXene (Ti 0.5 V 0.5 ) 3 C 2 is successfully synthesized by exfoliating a solid-solution MAX phase (Ti 0.5 V 0.5 ) 3 AlC 2 , 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 (Ti 0.5 V 0.5 ) 3 C 2 , which exhibits a better catalytic activity than that of Ti 3 C 2 . The addition of 10 wt% (Ti 0.5 V 0.5 ) 3 C 2 remarkably reduces the dehydrogenation onset temperature of MgH 2 by 70 °C, from 266 to 196 °C. At 250 °C, approximately 5.0 wt% H 2 is released from the 10 wt% (Ti 0.5 V 0.5 ) 3 C 2 -containing MgH 2 within 20 min. The dehydrogenated sample rapidly absorbs 4.8 wt% H 2 within 5 s at 120 °C; these hydrogenation kinetics are much more superior even to the well-studied Nb 2 O 5 catalyst. The apparent activation energy is calculated to be 77.3 kJ/mol for the MgH 2 -10 wt% (Ti 0.5 V 0.5 ) 3 C 2 sample, which is only around half of that of the pristine MgH 2 (153.8 kJ/mol). This is responsible for the remarkably reduced dehydrogenation operating temperature. Moreover, the chemical states of (Ti 0.5 V 0.5 ) 3 C 2 during dehydrogenation are also analysed and discussed.