H2 Interaction with C2H2TM (TM = Sc, Ti, V) Complex Using Quantum Chemical Methods

This work reports a comparative study of hydrogen uptake capacity of early transition metal atom (Sc, Ti and V) attached to light acetylene (C2H2) substrate. Using density functional theory and second order Moller-Plesset method, we predict that maximum of five, five and four hydrogen molecules will be adsorbed on C2H2Sc, C2H2Ti and C2H2V complex, respectively, with respective gravimetric hydrogen uptake capacity of 12.43, 12, and 9.48 wt%. All the interactions between hydrogen molecules and organometallic complex are found to be attractive. The highest occupied molecular orbital-lowest unoccupied molecular orbital gap shows that the maximum H-2 adsorbed complexes are kinetically stable. The average binding energies per H-2 molecule for these complexes are within the ideal range for hydrogen storage at ambient conditions. Even after maximum hydrogen molecules adsorption on C2H2TM complexes, transition metal atoms remain strongly bound to the C2H2 substrate. We have obtained temperature and pressure range over which H-2 adsorption on these three complexes is energetically favorable using the Gibbs free energy corrected H-2 adsorption energy.