BN-analogue of [2,2]paracyclophane functionalized with Sc and Ti for hydrogen storage

Abstract

Use of metal functionalized molecules for reversible hydrogen storage is well established due to their high gravimetric hydrogen storage capacity. We study BN-analogue of [2,2] paracyclophane (BNP22) containing two borazine rings and functionalized with Sc and Ti atoms to interpret its hydrogen binding capacity. First principles calculations based on density functional theory suggest that BNP22-2Sc and BNP22e2Ti systems can have a gravimetric density as high as 8.9 and 9.9 %, respectively. The BNP22-2Sc system can be operated under ambient thermodynamic conditions within the allowable pressure range of 3e30 atm and van ‘t Hoff desorption temperature range of 219e438 K as confirmed from molecular dynamics and occupation number studies. Both the systems establish BrønstedEvans-Polanyi relation with BNP22-2Sc having significantly less activation energy of 0.38 eV. We discuss the energetic stability of these systems with respect to vibrational frequency, absolute hardness, and transition states. Consistent with 2020 targets set by the DOE, BNP22-2Sc proves to be budding hydrogen storage material