Amol Deshmukh

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 H2 molecules can be adsorbed on unsubstituted C6H6Sc, C6H6Ti and C6H6V complexes, respectively, whereas upon boron substitution one additional H2 molecule gets adsorbed on each of these complexes. The H2 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 H2 adsorption on C4B2H6Sc is energetically unfavorable whereas it is favorable on C4B2H6Ti and C4B2H6V at ambient conditions. Various interaction energies for the H2 adsorbed complexes are obtained using a many-body analysis technique. The H2 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 H2 molecules in C4B2H6Sc(5H2) and C4B2H6Ti(5H2) complexes fly away during the simulation, thereby showing lower H2 uptake capacity of these complexes than that obtained by electronic structure calculations.

Closoborate-transition metal complexes for hydrogen storage

We report hydrogen uptake capacity of early transition metal (TM) atom (Sc, Ti and V) decorated closoborate (B6H6) using density functional theory and second order Moller–Plesset method. Maximum of four hydrogen molecules can be adsorbed on B6H6Sc, B6H6Ti and B6H6V complex with their gravimetric hydrogen uptake of 6.51, 6.36, 6.21 wt% respectively. We have used M06, B3LYP and MP2 methods with 6-311++G** basis set for the study. The Gibbs free energy corrected adsorption energies show that adsorption of four H2 molecules on B6H6Ti and B6H6V is energetically favorable whereas it is unfavorable on B6H6Sc at 298.15 K at M06/6-311++G** and B3LYP/6-311++G** level. Many-body analysis approach has been used here to study the nature of interaction between adsorbed H2 molecules and the substrate and that between hydrogen molecules in a complex. The binding energy of B6H6Sc(4H2), B6H6Ti(4H2) and B6H6V(4H2) complex is found to be 39.44, 58.43 and 51.03 kcal mol−1 respectively using M06/6-311++G** level of theory. Interaction between inorganic material-metal complexes with adsorbed H2 molecules is found to be attractive for all the three complexes. The charge transfer between Ti and adsorbed H2 molecules is more than that for Sc and V. The HOMO–LUMO gap shows that all the three H2 adsorbed complexes are kinetically stable. The dimers of TM-closoborate complexes in head-to-tail type configuration and multi-transition metal atom decorated closoborate complexes have also been studied. In both the cases number of H2 molecules adsorbed per TM atom is not affected neither by dimerization nor multi-transition metal atom decoration.

Tunable Gravimetric and Volumetric Hydrogen Storage Capacities in Polyhedral Oligomeric Silsesquioxane Frameworks

We study the hydrogen adsorption in porous frameworks composed of silsesquioxane cages linked via boron substituted aromatic structures by first-principles modeling. Such polyhedral oligomeric silsesquioxane (POSS) frameworks can be further modified by decorating them with metal atoms binding to the ring structures of the linkers. We have considered Sc- and Ti-doped frameworks which bind H2 via so-called Kubas interaction between hydrogen molecules and transition metal atoms. It will be demonstrated that the maximum H2 gravimetric capacity can be improved to more than 7.5 wt % by using longer linkers with more ring structures. However, the maximum H2 volumetric capacity can be tuned to more than 70 g/L by varying the size of silsesquioxane cages. We are optimistic that by varying the building blocks, POSS frameworks can be modified to meet the targets for the gravimetric and volumetric capacities set by the U.S. Department of Energy.