Enhanced reversible hydrogen storage properties of wrinkled graphene microflowers confined LiBH4 system with high volumetric hydrogen storage capacity

LiBH₄ with high hydrogen storage density, is regarded as one of the most promising hydrogen storage materials. Nevertheless, it suffers from high dehydrogenation temperature and poor reversibility for practical use. Nanoconfinement is effective in achieving low dehydrogenation temperature and favorable reversibility. Besides, graphene can serve as supporting materials for LiBH₄ catalysts and also destabilize LiBH₄ via interfacial reaction. However, graphene has never been used alone as a frame material for nanoconfining LiBH₄. In this study, graphene microflowers with large pore volumes were prepared and used as nanoconfinement framework material for LiBH₄, and the nanoconfinement effect of graphene was revealed. After loading 70 wt% of LiBH₄ and mechanically compressed at 350 MPa, 8.0 wt% of H₂ can be released within 100 min at 320 °C, corresponding to the highest volumetric hydrogen storage density of 94.9 g H₂ L⁻¹ ever reported. Thanks to the nanoconfinement of graphene, the rate-limiting step of dehydrogenation of nanoconfined LiBH₄ was changed and its apparent activation energy of the dehydrogenation (107.3 kJ mol⁻¹) was 42% lower than that of pure LiBH₄. Moreover, the formation of the intermediate Li₂B₁₂H₁₂ was effectively inhibited, and the stable nanoconfined structure enhanced the reversibility of LiBH₄. This work widens the understanding of graphene's nanoconfinement effect and provides new insights for developing high-density hydrogen storage materials.