Calcium decoration of boron nitride nanotubes with vacancy defects as potential hydrogen storage materials: A first-principles investigation

Hydrogen adsorption and storage performance of Ca-decorated boron nitride nanotubes (BNNTs) with vacancy defects are investigated theoretically using the first-principle calculation. Three types of experimentally available defects, B monovacancy (V-B), N monovacancy (V-N) and B?N divacancy (V-NB), are considered. The Ca atom prefers to reside on the vacancy site of BNNTs-V-B and BNNTs-V-BN without the problem of aggregation. The H-2 adsorption results indicate that six H-2 can be adsorbed by a Ca atom with the average adsorption energy slightly larger than 0.20 eV/H-2. The hydrogen gravimetric density is 6.4 wt.% and 6.9 wt.% for 8Ca/BNNT-V-B and 8Ca/ BNNT-V-BN systems, respectively. The polarization interaction and the weaker orbitals hybridization between Ca and H-2 are responsible for the hydrogen adsorption. The stability of the H-2 adsorbed complexes is also investigated by considering the temperature and pressure. The results indicate that the H-2 adsorbed structures of Ca-decorated BNNSs with V-B and V-BN defects are stable at room temperature under commonly used mild pressure.