Novel 1D carbon nanotubes uniformly wrapped nanoscale MgH2 for efficient hydrogen storage cycling performances with extreme high gravimetric and volumetric capacities

Magnesium hydride (MgH2) offers large capacity for hydrogen storage, but poor thermodynamics and kinetics for releasing hydrogen. In this work, the novel 1D bamboo-shaped carbon nanotubes (BCNTs) are firstly used as carriers for the self-assembly of MgH2 (denoted as MgH2@BCNTs). The high specific surface area (262.3 m(2)g(-1)) and large diameter (over 80 nm) of BCNTs contribute to extremely high loading capacity (76.8 mass fraction), small particle size (15-20 nm) and uniform distribution of MgH2 nanoparticles (NPs). The well-defined MgH2@BCNTs shows remarkably improved thermodynamics and kinetics for H-2 adsorption and desorption. In particular, it starts to release hydrogen at about 220 degrees C, near 170 degrees C lower than that of the commercial MgH2, as well it tends to be hydrogenated even at a relatively low temperature of 100 degrees C by absorbing 3.56 wt% H-2. Moreover, a reversible capacity up to 5.79 wt%, including the "dead weight" of BCNTs, and is well maintained after 10 cycles. The dehydrogenation E-a and Delta H of MgH2@BCNTs can be reduced to 97.97 kJ/mol and 68.92 kJ/mol, which are 111.24 kJ/mol and 6.07 kJ/mol lower than those of the commercial MgH2, respectively. By high pressure densification treatment, the MgH2@BCNTs system achieves an exceptional volumetric capacity up to 65.90 g/L without obvious performance degeneration, resulting from the special structure of BCNTs with inner intervals which works as supports under ultra-high pressure of 750 MPa. Our innovative design of 1D BCNTs supporting MgH2 NPs with high loading weight offers new strategy to synchronously improve the gravimetric and volumetric capacity, as well as the hydrogen storage kinetics and thermodynamics of the nanoconfinement system in the future.