Hydrogen storage on tin carbide monolayers with transition metal adatoms

In this work, we employ Density Functional Theory to study the effects of decoration with transition metal (TM) atoms—Ag, Au, Cu, Sc, Ti and Pd—on the H₂ adsorption properties of tin carbide monolayers (SnC-ML), as a prospective material for hydrogen storage. The results indicate that TM adatoms are strongly bonded to the SnC-ML and that electronic charge is transferred from the adatoms to the SnC-ML. In particular, it is found that Sc and Ti are chemisorbed on SnC-ML with strong binding energies. The most stable adsorption site for these metal atoms is above Sn atoms of the SnC-ML. Also, these TM atoms exhibit the higher hydrogen-storage capacities with up to four hydrogen molecules per adatom. In contrast, the other studied metals have at most 2 hydrogen molecules adsorbed. Approximate temperature- and pressure-dependent curves suggest that, to storage hydrogen, Sc- and Ti-decorated SnC-ML should be cooled under freezing temperatures, or kept at 1 MPa and 2.5 MPa, respectively, which are much lower pressures than those currently used in vehicular tanks, which attain pressures of 35 MPa. These results indicate that Sc and Ti decorated SnC-ML can be useful as hydrogen-storage solid-state devices.