Vijayanand Kalamse

Hydrogen uptake capacity of C2H4Sc and its ions: A density functional study

We report the gravimetric hydrogen uptake capacity of C2H4Sc complex and isoelectronic ions using Density Functional Theory. We predict that C2H4Sc+ can bind maximum seven hydrogen molecules in dihydrogen form giving gravimetric uptake capacity of 16.2 wt %, larger by about 2 and 4 wt % than the neutral and anion, respectively. We also found that the interaction of hydrogen molecules with C2H4Sc+ ion is characteristically different than that with neutral and anion. Vibrational spectroscopic study reveals that C2H4Sc and isoelectronic ions are quantum mechanically stable with their characteristic change in respective identified mode. The large gravimetric H2 uptake capacity of C2H4Sc+ is well above the target specified by Department of Energy (DOE) by 2015.

Verification of DFT‐predicted hydrogen storage capacity of VC3H3 complex using molecular dynamics simulations

Density functional theory (DFT) and Fourth‐order Möller–Plesset (MP4) perturbation theory calculations are performed to examine the possibility of hydrogen storage in V‐capped VC3H3 complex. Stability of bare and H2 molecules adsorbed V‐capped VC3H3 complex is verified using DFT and MP4 method. Thermo‐chemistry calculations are carried out to estimate the Gibbs free corrected averaged H2 adsorption energy which reveals whether H2 adsorption on V‐capped VC3H3 complex is energetically favorable, at different temperatures. We use different exchange and correlation functionals employed in DFT to see their effect on H2 adsorption energy. Molecular dynamic (MD) simulations are performed to confirm whether this complex adsorbs H2 molecules at a finite temperature. We elucidate the correlation between H2 adsorption energy obtained from density functional calculations and retaining number of H2 molecules on VC3H3 complex during MDs simulations at various temperatures.

Can ionization induce an enhancement of hydrogen storage in Ti2–C2H4 complexes?

We predicted here gravimetric hydrogen storage capacity of Ti2–C2H4 and Ti2–C2H4+ complexes using density functional theory (DFT) method. The number of adsorbed H2 on Ti2–C2H4 is limited to ten. It has been seen that controlling the charge-state of this complex enhances its gravimetric hydrogen uptake and the metal bond strength. The resulting cationized complex then adsorbs two additional H2 molecules than the neutral complex. In addition, we elucidated the effect of exchange and correlation functionals in DFT on H2 adsorption energy of these complexes. Molecular dynamics simulations were also carried out to confirm whether the complex adsorbs H2 molecules at a finite temperature. The H2 uptake capacity of a complex from simulations is the same as that from the geometry optimization only if the H2 adsorption was energetically favourable i.e. with the positive Gibbs free corrected H2 adsorption energy.

Hydrogen storage in C3Ti complex using quantum chemical methods and molecular dynamics simulations

The hydrogen storage capacity of C3Ti and C3Ti+ complex was studied using second order Møller-Plesset (MP2) and density functional theory (DFT) methods with different exchange and correlation functionals. Four and five H2 molecules can be adsorbed on C3Ti and C3Ti+ complex respectively at all the levels of theory used. This corresponds to the gravimetric H2 uptake capacity of 8.77 and 10.73 wt % for the former and the latter respectively. The nature of interactions between different molecules in H2 adsorbed complexes is also studied using many-body analysis approach. In the case of C3Ti(4H2) complex, total five-body interactions is negligible whereas for C3Ti+(5H2) relaxation energy is negligible. All the many-body energies have significant contribution to the binding energy of a respective complex. Atom-centered density matrix propagation molecular dynamics simulations were carried out using different methods to confirm whether H2 molecules remain adsorbed on C3Ti and C3Ti+ complex at room temperature. Adsorption Gibbs free energies show that four and five H2 molecule adsorption on C3Ti and C3Ti+ at room temperature is energetically favorable and unfavorable respectively using MP2 as well as DFT methods used here. H2 adsorption is thermodynamically favorable over a wide range of temperature on the C3Ti than C3Ti+complex.

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.

Hydrogen storage in neutral and charged metalized-C n H m (for n=m and n≠m) compounds

Density functional and MP2 calculations were used study the molecular hydrogen adsorption on C<inf>2</inf>H<inf>4</inf>Ti, C<inf>2</inf>H<inf>4</inf>Li<inf>2</inf> complexes and their charged state. The dependence of H<inf>2</inf> adsorption energy on the computational methods was studied. Thermo-chemistry calculations were performed to see whether H<inf>2</inf> adsorption on the complexes is energetically favorable at finite temperature or not. Molecular dynamic simulations were also performed to confirm the possibility of H<inf>2</inf> storage in the neutral and charged metalized complex at finite temperature.