Tin carbide monolayers decorated with alkali metal atoms for hydrogen storage

In this work, a density-functional study of hydrogen storage in tin carbide monolayers (2DSnC) decorated with alkali metals atoms (AM) such as Li, Na, and K, is reported. The most stable adsorption site for these alkali metal atoms on the 2DSnC is above a tin atom. The results indicate that the alkali metal atoms are chemisorbed on the 2DSnC and that electronic charge is transferred from the decorating atom to the 2DSnC. In all the studied cases, the hydrogen molecules are physisorbed on the AM-2DSnC (AM = Li, Na, and K) complexes and then these systems could be used for hydrogen storage. In particular, it is found that the K-2DSnC monolayer has the highest hydrogen-storage capacity, where a single potassium atom can adsorb up to 6 hydrogen molecules, followed by Na-2DSnC with 5 hydrogen molecules and Li-2DSnC with 3 hydrogen molecules. Finally, it can be estimated that when the K, Na and Li adatom-coverings respectively attain 40%, 44% and 70%, the hydrogen-storage gravimetric capacities of AM-2DSnC could overcome the US-DOE recommended target of 5.5 wt% for onboard automotive systems.