The high-capacity hydrogen storage of B6Ca2 and B8Ca2 inverse sandwiches

Abstract

The B6Ca2 and B8Ca2 clusters adopt interesting inverse sandwich architectures, featuring a prolate B6 (or perfect B8) ring jammed with two capping Ca atoms. Both clusters show the high thermodynamic stability due to the double (σ and π) electronic delocalization. In present paper, we computationally studied the hydrogen storage of them. The results suggest that each Ca site in B6Ca2 and B8Ca2 clusters could store up six H2, yielding a gravimetric density of 14.2 wt% for B6Ca2 and 12.6 wt% for B8Ca2. The average adsorption energy for H2-adsorbed B6Ca2 and B8Ca2 complexes is within the scope of 0.12–0.15 eV per H2 at wB97XD level, hinting that two clusters could reversibly store and release hydrogen, which is positively confirmed by the Born-Oppenheimer molecular dynamics simulations. Both B6Ca2 and B8Ca2 nanoclusters are feasible hydrogen storage media under the ambient condition.