Cubic NaNbO3 synthesized by alkali treatment of Nb2C MXene for enhancing the hydrogen storage of MgH2

Magnesium hydride (MgH 2 ) is a solid-state hydrogen storage material with promising applications. However, its slow hydrogen release rate at low temperatures (<573 K) and high hydrogen release energy barrier severely limit its practical applications. In this work, a bimetallic oxide (cubic NaNbO 3 ) with side length of 1–10 μm was derived from Nb 2 CT x MXene through a simple hydrothermal reaction, which has a high catalytic activity. The MgH 2 -5 wt% NaNbO 3 composite can rapidly release 6.18 wt% H 2 in 12 min at 260 °C and uptake 3.45 wt% H 2 in 90 min at 30 °C. The activation energy for dehydrogenation (E a ) of MgH 2 -5 wt% NaNbO 3 composite was calculated to be 84.72 kJ/mol, which is much lower than that of milled MgH 2 (150.98 kJ/mol). In addition, hydrogenation and dehydrogenation cycling test results indicated that the composite material presents excellent stable cycling durability, with a capacity retention rate of 99.7 % after 40 cycles, with almost no capacity degradation. The excellent hydrogenation and dehydrogenation ability is mainly contributed by the combined effect of NaMgH 3 , NaNbO 3 , Nb metal and NbH x . The results of this work are instructive for the design of high-properties catalysts to enhance the hydrogen storage capacity of Mg/MgH 2 system.