Spatial Confinement of Lithium Borohydride in Bimetallic CoNi-Doped Hollow Carbon Frameworks for Stable Hydrogen Storage

While lithium borohydride is one of the most promising hydrogen storage materials due to its ultrahigh hydrogen storage density, high thermodynamic stability, kinetic barriers, and poor reversibility, it is far from being used in practical applications. Herein, we prepare a cubic hollow carbon dodecahedron uniformly modified with a bimetallic CoNi alloy (CoNi/NC) for preserving the stable catalytic effect of CoNi alloys toward reversible hydrogen storage. It is theoretically confirmed that bimetallic CoNi alloys effectively weaken the B-H bonds of LiBH₄ by extending their average length to 1.33, 0.09 and 0.04 Å longer than that of LiBH₄ and LiBH₄ under metallic Co, respectively. More importantly, the alloying of Co with Ni avoids the reattachment of H from LiBH₄ to the Co surface, which prevents LiBH₄ from dehydrogenation for the formation of H₂ on the Co surface, thus resulting in an ultralow hydrogen desorption energy of 0.1, 1.85 and 0.52 eV lower than that of LiBH₄ and LiBH₄ under metallic Co. Therefore, the onset and peak hydrogen desorption temperatures decrease to 130 and 355 °C, respectively, 170 and 97 °C lower than that of bulk LiBH₄. More importantly, a reversible H₂ capacity of 9.4 wt % is achieved even after 10 cycles.