Elucidating hydrogen storage properties of two-dimensional siligraphene (SiC8) monolayers upon selected metal decoration

Abstract

Density functional theory calculations with dispersion corrections were employed to investigate the hydrogen (H₂) adsorptive properties of siligraphene (SiC₈), pristine and decorated with selected alkali (Li, Na, and K) and alkaline-earth (Be, Mg, and Ca) metals. We found that all the considered metals (Me), except Mg and Be, bind strongly to SiC₈ even at high doping concentrations (SiC₈Me₂) by donating a major portion of their valence electrons to SiC₈. Ab initio molecular dynamics (AIMD) simulations confirmed the thermal stabilities of SiC₈Me₂ (Me = Li, Na, K, Ca) at 300 K. We showed that Li, Na, and Ca-doped SiC₈ adsorbed multiple H₂ molecules with binding energies (E_bind) at least two times stronger than that of the pristine SiC₈ (E^pristine_bind = −70 meV per H₂). Overall, both SiC₈Li₂ and SiC₈Ca₂ adsorbed two and four H₂ molecules per metal adatom, respectively, having E_bind within the desirable range for an effective adsorption/desorption process. The resulting gravimetric densities of SiC₈Li₂ and SiC₈Ca₂ were 5.5 wt% and 7.3 wt%, respectively, surpassing the U.S. Department of Energy's 2025 goal of 5.5 wt%. The estimated H₂ desorption temperatures exceed substantially the boiling point of liquid nitrogen, confirming the potential of light metal decorated SiC₈ as a promising material for H₂ storage.