Synergistic H₂─CH₄ Co-Adsorption on Scandium-Decorated [5]Cycloparaphenylene Nanohoops for Gas Storage Application

This work presents computational insights into the cooperative adsorption and storage of hydrogen and methane gas in scandium (Sc) decorated [5]cycloparaphenylene ([5]CPP) nanohoops using first principles calculations supplemented with Grimme's dispersion correction (DFT+D3). The Sc atoms were functionalized over the [5]CPP molecule with an average binding energy of 1.53 eV. A single Sc atom can store up to five hydrogen molecules and four methane molecules in quasi-molecular form. The calculated average adsorption energies vary between 0.21 and 0.353 eV/H₂ and 0.263 and 0.243 eV/CH₄. At low temperature and pressure, the system exhibits a maximum gravimetric capacity of 7.68 wt% and 34.64 wt% for hydrogen and methane, respectively. The calculated van't Hoff temperature for hydrogen molecules shows a minimum at 296.9 K under 1 atm pressure. The desorption of H₂ molecules from the [5]CPP starts at around 300 K, and complete desorption occurs at more than 500 K. The host system is thermally stable, as evidenced by the atom-centered density matrix propagation molecular dynamics (ADMP-MD) simulations at different temperatures. Our calculations predict that Sc-functionalized [5]CPP can be a promising catalyst for efficient H₂ and CH₄ storage, providing useful insights for its applications in sustainable energy.