Graphene-induced growth of N-doped niobium pentaoxide nanorods with high catalytic activity for hydrogen storage in MgH2

Abstract

High operation temperatures and slow kinetics remain big challenges for using magnesium (Mg) as a practical hydrogen storage medium. In this work, a novel graphene-guided nucleation and growth process was developed for the preparation of N-doped Nb2O5 nanorods that enable remarkably improved hydrogen storage properties of MgH2. The nanorods were measured to be 10–20 nm in diameter. MgH2 doped with 10 wt% of the nanorods released 6.2 wt% H2 from 170 °C, which is 130 °C lower than additive-free MgH2, thanks to a 40% reduction in the kinetic barriers. About 5.5 wt% of H2 was desorbed in isothermal dehydrogenation test at 175 °C. Reloading of hydrogen was notably completed at 25 °C under 50 atm of hydrogen pressure, which has not been reported before. Density functional theory (DFT) calculations demonstrate the extended bond lengths and weakened bond strengths of Mg-H or H-H when MgH2/H2 adsorbs on the Nb-N-O/graphene model, consequently favouring lower operating temperatures and improved kinetics for hydrogen storage in MgH2 catalyzed by the graphene-guided N-Nb2O5 nanorods. Our findings provide useful insights in the design and preparation of high-performance catalysts of transition metals and rare metals for on-board hydrogen storage.