Accurate prediction of hydrogen storage capacity of small boron nitride nanocages by dispersion corrected semi-empirical PM6-DH2 method

Abstract

In this study, we have studied endohedral hydrogen storage capability of several selected BmNm nanocages (m = 12, 24, 36, 48 and 96) and their durability against hydrogen doping by the dispersion corrected semi-empirical PM6-DH2 method. Firstly, we determined performances of the PM6-DH2, PM7, B3LYP methods against the ωB97X-D method, which can make accurate estimations for systems including non-covalent interactions, and found out that PM6-DH2 predicted the stabilities of moderate sized hydrogen doped BN nanocages as accurately as ωB97X-D with computation times of several thousand times faster. Therefore, PM6-DH2 was employed to determine endohedral hydrogen storage capability of BmNm nanocages. It predicted that B24N24, B36N36, B48N48, and B96N96 nanocages have rather significant hydrogen storage percentages of 4.40, 6.67, 8.12 and 12.01%, respectively and B96N96 can endohedrally store up to 142H2 molecules. Analysis of destabilization energies of the complexes encapsulating maximum number of H2 molecules indicated that B24N24 and B48N48 are more durable than B36N36 and B96N96 against hydrogen doping because they can both highly inflate and quite compress hydrogen molecules. In addition, the B–N bond breaking energy for B96N96 is much smaller than the passage barrier of a hydrogen molecule through hexagonal holes, so nanocage breaks instead of hydrogen molecules escaping through the hole. According to all these findings, BN nanocages and larger structures built from them might be considered as good candidates for hydrogen storage.