First principles study of alkali metal-decorated bismuth selenide for hydrogen storage applications

The identification of novel two-dimensional materials is often highly valued because of their extraordinary characteristics and prospective uses. This study presents a new bismuth selenide (Bi₂Se₃) monolayer based on density functional theory (DFT). Its bandgap, state density, and mobilities are determined and examined. This study investigates hydrogen storage in Bi₂Se₃ adorned with alkali metal (Li/Na and K) atoms. The optimal adsorption site for alkali metal (AM) atoms on the Bi₂Se₃ monolayer is located above an Se atom. The AM atoms are physically adsorbed on Bi₂Se₃, and the electronic charge shifts from these to the Bi₂Se₃ monolayer. In all scenarios examined, hydrogen molecules are physically adsorbed onto AM–Bi₂Se₃ complexes, suggesting that these systems could be employed for hydrogen storage. The K–Bi₂Se₃ monolayer shows the highest hydrogen storage capacity, with one potassium atom adsorbing up to 19 hydrogen molecules, while both Na–Bi₂Se₃ and Li–Bi₂Se₃ could adsorb 18 hydrogen molecules. It is estimated that the hydrogen-storage gravimetric capacities of AM–Bi₂Se₃ are within the US-DOE criteria, where the adatom coverage reaches about 6.71 wt% for K, 6.52 wt% for Na, and 6.66 wt% for Li.