Synergetic action of 0D/2D/3D N-doped carbon nanocages and NbB2 nanocatalyst on reversible hydrogen storage performance of lithium borohydride

A synergetic approach of nanoconfinement coupling with in-situ formed nanocatalysts was developed to fabricate a novel and robust nano-LiBH4 system. The nanoconfining scaffold exhibits an unparalleled 3D hierarchical architecture featuring micro-, meso-, and macro-pores assembled by 2D interconnected nanosheets that consist of 0D hollow nitrogen-doped carbon nanocages. This structure possesses an accumulated pore width of 7.79 nm, extremely high pore volumes of 3.16 cm3/g, and a theoretical loading capacity of 67.9 wt% for LiBH4. The in-situ formed NbB2 species transformed from initial NbF5 nanoparticles is confirmed as the final active nanocatalyst. It is worth mentioning that the defective N heteroatoms within the scaffold can serve the role of coordinating with Nb cations and weaken the B-H bonds as supported by the DFT calculations. With an optimized loading of 50 wt% LiBH4, the initial dehydrogenation temperatures can be reduced to 140.6 °C, and the system can rapidly release 7.55 wt% H2 at 320 °C within 39 min. Furthermore, the nanoconfined system exhibits excellent low-temperature reversibility, retaining 93 % of its capacity after 20 cycles at 300 °C. This study provides innovative perspectives on the design of novel scaffold structures doped with defective heteroatoms for the nanoconfinement and synergetic catalysis of de/rehydrogenation for metal borohydrides.