A theoretical modelling of NaBr(H₂)_n clusters as an approach in hydrogen gas storage

Adsorption of H₂ on a bed of NaBr for the formation of NaBr(H₂)_n (n = 1–8) aggregates is reported here theoretically. Second-order Moller–Plesset perturbation calculations were carried out using the MP2/aug-cc-pVDZ level for predictions of adsorption energies and Gibbs free energy changes for these aggregates. The NaBr(H₂)_n aggregates are predicted to steadily increase in H₂ saving capacity and energy efficiency as n increases from 1 to 8, relative to free H₂ molecules under identical conditions. The low activation energies for H₂ desorption from the NaBr(H₂)_n adducts result in high amounts of H₂ molecules desorbed at low temperatures. The vibrational stretching frequencies of H₂ (H–H) show a red shift. The Natural Bond Orbital calculations were used to investigate the nature of NaBr···H₂ interactions. Furthermore, cooperativity was predicted as a result of the stabilization energy of complexes and is discussed. Finally, electronic properties of the NaBr(H₂)_n clusters were obtained by the density of states calculation.