First-principles study of hydrogen storage on Ca-decorated defective boron nitride nanosheets

Abstract

Hydrogen storage on the Ca-decorated defective boron nitride nanosheets (BNNSs) is investigated by first-principle calculation based on density functional theory. Four types of experimentally available defects, B vacancy (VB), N vacancy (VN), Stone-Wales defect (SW) and B–N divacancy (VNB), are considered. It is found that the binding energy of Ca atom on BNNSs with VN and SW defects is smaller than the cohesive energy of bulk Ca. While the Ca atom has strong bonding strength with BNNSs with VB and VBN defects without the problem of aggregation. Six H2 molecules can be absorbed by a Ca atom with the average adsorption energy of 0.206–0.242 eV/H2. The Ca decorated on both sides of BNNSs with VB and VBN defects leads to the hydrogen gravimetric density of 7.6 wt% and 8.0 wt%, respectively. Both the polarization mechanism and the weaker hybridization of Ca-3d orbitals with H-s orbitals are responsible for the adsorption of H2 molecules. The effect of temperature and pressure on the hydrogen storage performance is also investigated, and the results indicate that the hydrogen adsorbed structures of Ca-decorated BNNSs with VB and VBN defects are stable at room temperature under mild pressure.