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

Abstract

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 C₆₀Ca_x, x = 1–6, C₄₈B₁₂Ca_x is stable with respect to decomposition into the fullerene molecules and Ca bulk metal. (4) C₄₈B₁₂Ca_x 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.