Three-Dimensional Porous Silicon-Carbon Polymorph: Li/Na Functionalization toward High-Efficiency Hydrogen Storage

Abstract Porous materials decorated with alkali metals have emerged as attractive candidates for reversible hydrogen storage because they can simultaneously provide high adsorption capacity, suitable adsorption strength, and rapid hydrogen transport. Motivated by this strategy, the present work explores the hydrogen-storage behavior of three-dimensional porous silicon-carbon polymorph 3D-t(SiC)12 after Li and Na functionalization using density functional theory (DFT) calculations together with ab initio molecular dynamics (AIMD) simulations. Both alkali metals interact strongly with the host framework, exhibiting binding energies of –2.58 eV for Li and –2.10 eV for Na, which indicates thermodynamically stable decoration and minimizes the tendency toward metal clustering. A clear distinction is observed between the two decorating species, with Li producing significantly stronger interactions with hydrogen molecules than Na. As a result, the Li-functionalized framework stores as many as 34 H2 molecules, corresponding to a gravimetric capacity of 6.39 wt %, while maintaining an average adsorption energy of –0.167 eV per H2, a value favorable for reversible adsorption and desorption. Under identical conditions, Na decoration yields a lower storage capacity of 5.86 wt %. Thermodynamic calculations predict hydrogen release within an average temperature window of 267–368 K and equilibrium pressures between 8 and 20 bar, highlighting practical operating conditions. Dynamic stability is confirmed by AIMD simulations, which show that the hydrogenated structures remain intact throughout the simulations while preserving reversible adsorption characteristics. In addition, hydrogen diffusion on the Li-decorated surface proceeds through remarkably small activation barriers of only 0.010–0.178 eV, suggesting highly efficient molecular transport across the porous network. Collectively, these findings demonstrate that Li-functionalized 3D-t(SiC)12 is a highly promising solid-state hydrogen-storage material and provide valuable design principles for next-generation porous hydrogen-storage materials.