Hydrogen Storage Capabilities of the Low-Lying Ca2B4 Clusters

The structural feature and electronic property of Ca2B4, as well as its potential for hydrogen storage, have been studied using density functional theory. The first, second, and fourth low.lying isomers Ca2B4 01, Ca2B4 02, and Ca2B4 04 have high stabilities in thermodynamics and can adsorb 12, 12, and 10 H-2 molecules with respective H-2 gravimetric uptake capacity of 16.3%, 16.3%, and 14.0%, which far exceeds the target (5.5%) proposed by the US department of energy (DOE). The average absorption energies per H2 molecule are in the range of 0.58.4.21 eV for Ca2B4 01(H-2)12, 0.54. 3.69 eV for Ca2B4 02(H-2)12, and 0.10. 0.12 eV for Ca2B4 04(H-2)10. Born. Oppenheimer molecular dynamic (BOMD) simulations indicate Ca2B4 01 and Ca2B4 02 are promising candidates for adsorbing hydrogen, but Ca2B4 04 is not. The results of hydrogen adsorption energies with Gibbs free energy correction indicate that 12 H-2 molecules on Ca2B4 01 and Ca2B4 02 are energetically favorable with a wide range of temperatures at 101 325 Pa.