Synthesis and Hydrogen Adsorption Simulation of Carbonized Hyper-Cross-Linked Polymers Derived from Various Green Flavonoid Monomers

Solid-state hydrogen storage offers advantages such as high volumetric density, mild operating conditions, and the potential for ultrapure hydrogen release. Here, a series of hyper-cross-linked polymers (HCPs) were synthesized from various renewable flavonoid monomers via the Friedel-Crafts reaction and subsequently carbonized, thereby enhancing graphitization and hierarchical porosity. Experimentally, apigenin-derived HCPs achieved a maximum hydrogen uptake of 0.86 wt % at 298 K and 80 bar. Complementary molecular simulations (ReaxFF-based molecular dynamics, density functional theory, and Grand Canonical Monte Carlo) were employed to elucidate the carbonization pathways, pore formation, and adsorption behavior. The simulations revealed that carbonization proceeds via C-O bond cleavage, dehydration, and condensation into naphthalene-like and graphitic microdomains. Density functional theory (DFT) simulations indicate the maximum hydrogen adsorption energy at the seven-membered ring and hexa-heptagonal junction. The GCMC simulations indicate that the daidzein-derived HCPs reproduced the experimental trends and predicted hydrogen uptakes up to 5.32 wt % at 77 K and 80 bar, approaching the U.S. Department of Energy target for onboard storage. This work demonstrates that carbonized flavonoid-based HCPs are promising, ecofriendly hydrogen adsorbents and provides mechanistic insights to guide the rational design of sustainable, high-performance storage materials.