Reversible hydrogen storage in Li-functionalized [1,1,1,1]paracyclophane: A computational insight

Abstract

This study focuses on investigating the hydrogen adsorption-desorption properties and storage capacities of Li functionalized [1,1,1,1]paracyclophane (PCP1111) using dispersion-corrected density functional theory and molecular dynamics simulation. The Li atom is bound to the [1,1,1,1]paracyclophane's benzene ring via Dewar mechanism, with a binding energy of 0.32 eV without any clustering. Each Li atom is found to adsorb 5H2 molecules, causing the host material PCP1111–4Li to adsorb up to 20H2 molecules via charge polarization with an average adsorption energy of 0.156 eV/H2, indicating physisorption type adsorption. The charge polarization during hydrogen adsorption is studied using Hirshfeld charge analysis and electrostatic potential maps. PCP1111–4Li saturated with 20H2 results in gravimetric densities as high as 9.4 wt%, which is considerably higher than the US-DOE target. During the H2 adsorption process, the host material's geometry does not change significantly, indicating its chemical stability. When the temperature exceeds 180 K under 30–60 bar, the gravimetric density decreases, but it is still greater than 5.5 wt%, which is the target set by the US Department of Energy for 2025. The maximum H2desorption temperature estimated by the Vant-Hoff relation is found to be 216 K and 266 K at 1 atm and 5 atm, respectively. ADMP molecular dynamics shows the structural integrity and reversibility of host materials.