Enhanced reversible hydrogen storage in LiBH4-Mg(BH4)2 composite with V2C-Mxene

Solid-state borohydride was one of the promising solid-state hydrogen storage materials, but the reversibility and kinetics of hydrogen de/absorption in borohydrides still need improvement. In this study, a new strategy of repeated ball milling and melting was first used to produce LiBH4-Mg(BH4)2 nanocomposites (LMBH) effectively loaded on V2C Mxene as the matrix. The LMBH-20V2C composite released 8.1 wt% of hydrogen at 350 °C while un-doped LMBH only released 4.3 wt% under the same conditions. Two-step dehydrogenation with lower activation energies (118.2 and 125.2 kJ/mol) were found in LMBH-V2C composites. More than 5 wt% reversible hydrogen capacity was discovered in LMBH-V2C samples, which was 138 % more than that of un-doped LMBH. The nano-sized LMBH-V2C composite retained unaggregated, and VH2.01 species was formed during cycling as an active "hydrogen pump". The outstanding hydrogen storage performance of LMBH-V2C composites could be attributed to the combination of nano-sizing and catalysis from V2C Mxene.