Enhanced hydrogen storage in alkali metal-decorated B4C3: A pathway towards high-capacity hydrogen storage

Realizing a hydrogen-based economy hinges on the development of affordable and high-performance hydrogen storage materials. This work reports hydrogen storage prospects of alkali metal atoms Li, Na and K decorated B₄C₃ monolayers based on first-principles calculations. The calculations reveal that the B₄C₃ monolayer, demonstrating robust and slightly buckled graphene-like structure (a direct bandgap of 1.91 eV), is an excellent matrix to store hydrogen. The pristine monolayer is capable to physiosorb up to 9 hydrogen molecules with an average adsorption energy of −0.09 eV, realizing a gravimetric density of 2.77 wt%, via induced charge polarization. The decoration of B₄C₃ with alkali metals (Li, Na, K) was carried out which caused bonding of the metal atoms on the surface of the monolayer with high binding energies ranging from −2.17 to −2.50 eV and without causing agglomeration. The decoration appeared to significantly enhance H₂ adsorption capacity of the material offering physisorption energies in range −0.42 to −0.58 eV. Li@B₄C₃ and Na@B₄C₃ could adsorb up to 5 whereas K@B₄C₃ store 6 hydrogen molecules under reversible physisorption at optimal adsorption energies (−0.10 to −0.60 eV) without notable structural distortion. The one-fourth metal covered monolayer exhibited significantly high densities of 6.79 wt% (4Li@B₄C₃), 7.19 wt% (4Na@B₄C₃), and 5.75 wt% (4K@B₄C₃), with desorption temperatures ranging from 185 K to 355 K (at 1 atm) pointing to practical utilization of the materials. The hydrogen-loaded decorated monolayers are thermally stable at room temperature, with the Na-decorated slab indicating gravimetric density of 7.19 wt% accompanied by practical desorption temperatures for reversible hydrogen storage, beating several contemporary materials.