Superior reversible hydrogen storage in eutectic LiBH4–KBH4 system via Ni–based catalysts synergized with graphene

Abstract

Light metal borohydrides are promising candidates for solid–state hydrogen storage due to their high hydrogen storage capacities; however, the reversibility and kinetics of de/hydrogenation still require significant improvement. The present work focuses on the improvement of the hydrogen storage properties of the eutectic borohydride system of LiBH₄–KBH₄ (Li/KBH₄). A layered composite of graphene supported with ultrafine Ni₃B nanoparticles (Ni₃B/G) is designed and synthesized, which acts as catalyst and confinement carrier for Li/KBH₄. Assisted with a heating of the mixture of Li/KBH₄ and Ni₃B/G to 110 °C in the molten state of Li/KBH₄, an interlayer structure of graphene dispersed with Ni₃B nanoparticles and sheet–like Li/KBH₄ is constructed. The graphene effectively disperses Ni₃B nanoparticles and confines the Li/KBH₄ in its interlayers. The confinement of Li/KBH₄ and the catalysis of Ni₃B nanoparticles, assisted with the high thermal conductivity of graphene, contribute synergistically the hydrogen storage of Li/KBH₄. The main dehydrogenation peak temperature of the system is lowered to 278 °C. The system can release 8.5 wt% H₂ within 30 min at 350 °C. The capacity retention achieves 81.2 % after 50 cycles. DFT theoretical analysis shows that there is strong charge transfer interaction between Ni₃B and LiBH₄/KBH₄, which destabilizes the [BH₄]^– structure and promotes the dehydrogenation. This work provides a new approach for the design of new structural LiBH₄–based eutectic system with high capacity, low dehydrogenation temperature, high reversibility and long cycling life.