Room-Temperature Reversible Hydrogen Storage in Scandium-Decorated [6]Cycloparaphenylene: Computational Insights

Abstract

This study discusses the hydrogen storage and delivery capacity of Sc-decorated [6]cycloparaphenylene ([6]CPP) using dispersion-corrected density functional theory calculations (DFT + D3). The scandium atoms are decorated over [6]CPP via Dewar coordination with an average binding energy of 1.33 eV. Each Sc atom stores up to 5H₂ molecules in quasi-molecular form at an average adsorption energy ranging from 0.23 to 0.36 eV/H₂. The system's stability before and after H₂ adsorption is checked using reactivity parameters. The maximum hydrogen gravimetric capacity of the system is found to be 7.68 wt% at low temperatures at 1–60 bar pressure. With an increase in temperature (300–420 K), the gravimetric density is more than 5.5 wt% (US-DOE target) below 60 bar. Atom-Centered Density Matrix Propagation (ADMP)-molecular dynamics (MD) simulations reveal that the desorption of H₂ molecules from [6]CPP starts at around 300 K/1 bar, and complete desorption occurs above 480 K. The minimum Van't Hoff desorption temperature for [6]CPP-Sc is 296.9 K at 1 atm pressure. Insignificant change in the structure of [6]CPP-Sc during adsorption and desorption processes promises stability and reversibility of the system. Hence, we believe that Sc-decorated [6]CPP can be a promising candidate for hydrogen storage applications.