Excellent catalytic activity of a two-dimensional Nb₄C₃T_x (MXene) on hydrogen storage of MgH₂

A two-dimensional Nb₄C₃T_x (MXene) prepared via a chemical exfoliation was applied into MgH₂ by ball milling. The activated MgH₂-5 wt%Nb₄C₃T_x composite exhibits superior hydrogen storage kinetics properties. The onset temperature for the activated MgH₂-5 wt%Nb₄C₃T_x composite is significantly reduced from 296.5 °C (the balled pure MgH₂) to 150.6 °C, representing a 145.9 °C reduction, and which can release completely within 800 s at 250 °C, with a larger rate constant of 1.09164 wt% min⁻¹. Additionally, the apparent activation energy for dehydrogenation of the activated MgH₂- 5wt%Nb₄C₃T_x composite is 81.2 kJ/mol H₂ much lower than that of the balled pure Mg (153.8 kJ/mol H₂). After dehydrogenation, the sample can absorb approximately 3.50 wt% hydrogen within 2 h at temperatures as low as 50 °C, and the apparent activation energy for hydrogenation decreases to 27.8 kJ/mol H₂ much lower than that of the dehydrogenated pure Mg (82.1 kJ/mol H₂). Such excellent hydrogen storage kinetics and lower energy barriers explain high catalytic activity derived from Nb₄C₃T_x towards the hydrogen storage reaction of MgH₂, which are likely due to the unique layered structure and in situ formed NbH_x. This research extends the knowledge of designing efficient catalyst via the two-dimensional MXene in the hydrogen storage materials.