Inducing One-Step Dehydrogenation of Magnesium Borohydride via Confinement in Robust Dodecahedral Nitrogen-Doped Porous Carbon Scaffold.

Abstract

A dodecahedral activated N-doped porous carbon scaffold is synthesized and used for the nanoconfinement of Mg(BH₄)₂. The optimized mesoporous scaffold possesses an accumulated pore width of 2.65 nm, high specific surface area (3955.9 m² g^-1), and large pore volume (2.15 cm³ g^-1), providing ample space for the confinement of Mg(BH₄)₂ particles and numerous surface active sites for interactions with the same. The confined Mg(BH₄)₂ system features a dehydrogenation onset temperature of 81.5 °C, an extremely high capacity of 10.2 wt% H₂, and an almost single-step dehydrogenation profile. Moreover, the system exhibits superior capacity retention of 82.7% after 20 cycles at a moderate temperature of 250 °C. Precise activation control enables a transformation from microporous carbon materials to mesoporous ones, and hence the efficient nanoconfinement of Mg(BH₄)₂ and realization of one-step dehydrogenation. The evolution of borohydride intermediates is systematically revealed throughout the cycling process. Density functional theory calculations demonstrate defective N heteroatoms within the scaffold are vital in reducing the strength of B─H bonds, and the N-doped carbon can facilitate decomposition of the irreversible MgB₁₂H₁₂ intermediate. This study opens up new avenues for designing robust carbon scaffolds doped with heteroatoms and analyzing intermediate evolution in nanoconfined Mg-based borohydride systems.