Mechanistic insights into the enhancement of MgH2 hydrogen storage performance by ultra-stable bimetallic Mo2V2C3 MXene

Abstract

Magnesium hydride, as an important light-metal hydrogen storage material for on-board hydrogen storage, aerospace, and energy fields, has long been limited in its large-scale applications by slow hydrogen storage speed and high dehydrogenation temperature. In this work, ultra-stable bimetallic MXene Mo₂V₂C₃ was successfully synthesized and used to accelerate the hydrogen storage speed and reduce the dehydrogenation/hydrogenation temperature of MgH₂. The MgH₂ + 10 wt% Mo₂V₂C₃ sample starts dehydrogenation at 180 °C and reaches the maximum dehydrogenation rate at 259 °C. It also exhibits outstanding room-temperature (RT) rapid hydrogenation performance and cycling stability, retaining up to 100% capacity after 50 cycles at 300 °C. Another interesting phenomenon is that the hydrogen storage speed of the sample is even faster without capacity decrease as the dehydrogenation/re-hydrogenation cycle proceeds. First-principles calculations show that the Mg atoms are stabilized at the top sites of Mo atoms, and the Mg–H bonds that are adsorbed on Mo₂V₂C₃ are more susceptible to breakage. The key to the accelerated rate of Mg/MgH₂ hydrogenation/dehydrogenation is the enhancement of the interaction between Mg/MgH₂ and Mo₂V₂C₃ MXene with the increasing number of cycles, whereas the existence of the V renders the structure of MXene more stable. Our study refines the mechanistic understanding of bimetallic MXene catalyst for MgH₂ hydrogen storage and expands reference on the type and preparation of bimetallic MXene.