Improved H2 uptake capacity of transition metal doped benzene by boron substitution

The effect of boron substitution on hydrogen storage capacity of transition metal (TM) doped benzene is studied using density functional theory and the second order Moller-Plesset method with aug-cc-pVDZ basis set. Out of the six carbon atoms in a benzene ring, two are substituted by boron atoms. The structures considered here are C4B2H6TM (TM = Sc, Ti, V). Four, four and three H-2 molecules can be adsorbed on unsubstituted C6H6Sc, C6H6Ti and C6H6V complexes, respectively, whereas upon boron substitution one additional H-2 molecule gets adsorbed on each of these complexes. The H-2 uptake capacity of C4B2H6Sc, C4B2H6Ti and C4B2H6V obtained is 7.71, 7.54 and 5.99 wt%, respectively. Gibbs free energy corrected adsorption energies show that H-2 adsorption on C4B2H6Sc is energetically unfavorable whereas it is favorable on C4B2H6Ti and C4B2H6V at ambient conditions. Various interaction energies for the H-2 adsorbed complexes are obtained using a many-body analysis technique. The H-2 desorption temperature for boron substituted TM doped benzene is lower than that for TM doped benzene for all the three systems. Molecular dynamics simulations show that loosely bonded H-2 molecules in C4B2H6Sc(5H(2)) and C4B2H6Ti(5H(2)) complexes fly away during the simulation, thereby showing lower H-2 uptake capacity of these complexes than that obtained by electronic structure calculations.