Abstract
Ab initio calculations are performed to study hydrogen storage properties of Ti-doped benzene and Ti-doped nitrogen-substituted benzene complexes. Two of the carbon atoms in benzene are replaced by two nitrogen atoms. Two nitrogen atoms are substituted either at 1-2, 1-3, or 1-4 positions of a benzene ring and named as BN1-2Ti, BN1-3Ti, and BN1-4Ti, respectively. Maximum four, four, three, and four H2 molecules get adsorbed on C6H6Ti, BN1-2Ti, BN1-3Ti, and BN1-4Ti complexes respectively with respective H2 uptake capacity of 6.02, 5.84, 4.45, and 5.84 wt%. The positive Gibbs free energy corrected H2 adsorption energy values obtained for all these complexes at ambient conditions indicate that the formation of these complexes at room temperature is thermodynamically favorable. Temperature- and pressure-dependent adsorption energy calculations show that the H2 adsorption on all these complexes is feasible over a wide range of temperature and pressure. The gap between the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbital (LUMO) is found to be greater than 5 eV for all the complexes indicating stability of these complexes. The H2 molecules interact more strongly with Ti-doped nitrogen-substituted benzene than the Ti-doped benzene that results in higher H2 desorption temperature obtained using van 't Hoff equation for the former than the latter. The density of states plots have been used to understand the H2 adsorption mechanism.
Published Version
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