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

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.

High-loading LiBH4 Confined in Structurally Tunable Ni Catalyst-decorated Porous Carbon Scaffold for Fast Hydrogen Desorption.

Catalysts combined with nanoconfinement can improve the sluggish desorption kinetics and poor reversibility of LiBH4 . However, at high LiBH4 loading, their hydrogen storage performance is significantly reduced. Herein, a porous carbon-sphere scaffold decorated with Ni nanoparticles (NPs) was synthesised by calcining a Ni metal-organic framework precursor, followed by partial etching of the Ni NPs to fabricate an optimised scaffold with a high surface area and large porosity that accommodates high LiBH4 loading (up to 60 wt.%) and exhibits remarkable catalyst/nanoconfinement synergy. Owing to the catalytic effect of Ni2 B (formed in situ during dehydrogenation) and the reduced hydrogen diffusion distances, the 60 wt.% LiBH4 confined system exhibited enhanced dehydrogenation kinetics with >87% of the total hydrogen storage capacity released within 30 min at 375 °C. The apparent activation energies were significantly reduced to 110.5 and 98.3 kJ/mol, compared to that of pure LiBH4 (149.6 kJ/mol). Moreover, partial reversibility was achieved under moderate conditions (75 bar H2 , 300 °C) with rapid dehydrogenation during cycling.