Functionalized tetrahedral silsesquioxane cages for hydrogen storage

Abstract

The hydrogen storage capacity of functionalized Tetrahedral Silsesquioxane (H4Si4O6) cages is obtained using density functional theory (M062X) and second order Møller-Plesset (MP2) method with 6-311++G∗∗ basis set. We labelled Tetrahedral Silsesquioxane (H4Si4O6) as ‘TS’. We replaced four hydrogen in TS one by one with C2HBe or C2HTi group and labelled as TSR1M1, TSR2M2 TSR3M3 and TSR4M4 where RM can be either C2HBe or C2HTi. In TSRM when one hydrogen in a cage is replaced by C2HBe or C2HTi maximum of two and five hydrogen molecules, get adsorbed per Be and Ti atom respectively with respective H2 capacity of 1.61 and 3.42 wt %. H2 uptake capacity of TSRmMm (m = 1, 2, 3 and 4) has increased extensively when all the hydrogen in cage are replaced either C2HBe or C2HTi. TSR4M4 with RM = C2HTi can adsorbs maximum of 20H2 molecules with highest H2 uptake of 7.46 wt % among all the studied complexes. Calculated Gibbs free energy corrected H2 adsorption energies show that adsorption of H2 molecules on all the complexes is thermodynamically favourable. The desorption temperature for the complexes were calculated by using the van't Hoff equation. Calculated interaction energies show that H2 molecules interact strongly with Be atom than Ti atom. The molecular dynamics (MD) simulations have also been performed using atom centered density matrix propagation (ADMP) at ambient conditions. Interaction of hydrogen molecules and the metal atom is confirmed through the density of states (DOS) plot.