Improved hydrogen storage in Ca-decorated boron heterofullerenes: a theoretical study

We computationally investigate the hydrogen storage properties of calcium-decorated C48B12 boron-carbon heterofullerene molecules, and compare them to C60 (all-carbon) fullerene decorated with calcium. We employ density functional theory (DFT) on the lowest energy configurations of C48B12 molecules and find that these molecules have the following properties. (1) The most stable C48B12 isomers have an electron affinity that is 0.93–1.04 eV higher than their carbon only counterpart. (2) The binding of a Ca atom to C48B12 is ∼2.2 eV stronger than its binding to C60. (3) Unlike C60Cax, x = 1–6, C48B12Cax is stable with respect to decomposition into the fullerene molecules and Ca bulk metal. (4) C48B12Cax binds up to six hydrogen molecules per metal center, leading to a gravimetric density of up to 7.1 weight percent (wt%). The hydrogen binding energies of up to ∼0.24 eV open a prospect of hydrogen storage at ambient temperature.