New Li-doped fullerene-intercalated phthalocyanine covalent organic frameworks designed for hydrogen storage

Abstract

Applying density functional theory (DFT) calculations, we have designed fullerenes (C₂₀, C₂₄, C₂₆, C₂₈, C₃₀, C₃₆, C₆₀ and C₇₀) intercalated phthalocyanine covalent organic frameworks (C_n-Pc-PBBA COFs). First principles molecular dynamics (MD) simulations showed that the structures of C_n-Pc-PBBA COFs are stable at room temperature and even at higher temperature (500 K). The interlayer distance of Pc-PBBA COF has been expanded to 7.48–13.25 Å by the intercalated fullerenes, and the pore volume and surface area were enlarged by 2.3–3.1 and 2.0–2.6 times, respectively. The grand canonical Monte Carlo (GCMC) simulations show that our designed C_n-Pc-PBBA COFs exhibit a superior hydrogen storage capability: at 77 K and P = 100 bar, the hydrogen gravimetric and volumetric uptakes reach 9.4–12 wt% and 48.1–52.2 g L⁻¹, respectively. To meet the requirement for practical application in hydrogen storage, we use the Li-doping method to modify the hydrogen storage performance of C_n-Pc-PBBA COFs. Our results show that the Li atoms can stably locate on the surface of C₃₀-, C₃₆, C₆₀ and C₇₀-Pc-PBBA COFs. At T = 298 K and P = 100 bar, for these four Li-doped C_n-Pc-PBBA COFs, the gravimetric and volumetric uptakes of H₂ reach 4.2 wt% and 18.2 g L⁻¹, respectively.