Catalytic effect of two-dimensional Mo2TiC2 MXene for tailoring hydrogen storage performance of MgH2

Two-dimensional Mo2TiC2 MXene material was synthesized by etching Mo2TiAlC2 and then doped into MgH2 to tailor its hydrogen storage performance. The initial hydrogen desorption temperature of the Mo2TiC2-doped MgH2 was significantly reduced from 330 degrees C (pristine MgH2) to 187 degrees C. Isothermal dehydrogenation analysis indicated that the MgH2+9 wt.% Mo2TiC2 composite rapidly discharged 6.4 wt.% H2 at 300 degrees C within 4 min. For hydrogenation, the dehydrogenated MgH2+9 wt.% Mo2TiC2 uptook 6.5 wt.% H2 at 175 degrees C within 5 min. By calculation, the activation energy for MgH2+9 wt.% Mo2TiC2 was calculated to be (135.6 +/- 1.9) kJ/mol for the desorption reaction and (46.1 +/- 0.2) kJ/mol for the absorption reaction. After 20 cycles, 1.0 wt.% H2 was lost for the MgH2+9 wt.% Mo2TiC2 composite. Microstructure analysis results showed that the presence of Mo in Mo2TiC2 enhanced the thermal stability of MXene and reduced the amount of active Ti during cycling, leading to poorer catalytic effect of the catalyst compared to Ti3C2.