Catalyzed eutectic LiBH4–KBH4 system nanoconfined at low temperature for superior hydrogen storage reversibility

Abstract

Lithium borohydride (LiBH₄) has a high theoretical hydrogen storage capacity, making it a promising candidate for hydrogen storage applications. However, it suffers from high thermal stability, poor kinetics and low reversibility. This work presents the construction of a low-melting-point dual-cation eutectic borohydride system composed of LiBH₄ and KBH₄ (Li/KBH₄), tactfully coupled with a low-melting-point catalytic additive, NiCp₂. The nanoconfinement of the borohydride into porous carbon scaffolds and the introduction of the catalytic additive are synchronously achieved by melt infiltration at an extremely low temperature of 175 °C. The temperature is over 100 °C lower than that for bare LiBH₄. This method is considerably simpler than those that generally require an additional step for catalyst introduction. The liquid states of both the borohydride and catalytic additive during the infiltration process facilitate uniform mixing, resulting in highly homogenous dispersed catalytic sites. A highly reversible intercalation/deintercalation of Li occurs at the interface between Li/KBH₄ and the carbon scaffold, contributing effectively to the hydrogenation/dehydrogenation cycles of Li/KBH₄. The dehydrogenation activation energy of the confined system is reduced by over 70 kJ mol⁻¹ compared to that of the pristine LiBH₄ or the Li/KBH₄ system. The confined system can release 7.0 wt% H₂ at 300 °C within 30 min and demonstrates a remarkable capacity retention of 94.3% after 50 cycles, outperforming all previously reported borohydride systems. The present work provides a new insight and a feasible approach for designing novel nano-sized borohydride structures coupled with catalysts for the development of high-performance hydrogen storage materials.