External electric field induced hydrogen storage/release on calcium-decorated single-layer and bilayer silicene

Hydrogen storage and release are two essential parameters that define the efficiency of a hydrogen storage medium. Herein, we investigate the effects of the external electric field F on the adsorption-desorption of H-2 on a Ca-decorated silicene system (Ca-silicene) based on density functional theory calculations. Our study demonstrates that nine H-2 molecules per Ca atom can be adsorbed and 6.4 wt% H-2 can be adsorbed on Ca-silicene with an average binding energy of 0.19 eV per H-2, while the appropriate F can be used to effectively enhance the hydrogen storage-release on the Ca-silicene system. The high synergetic effect may be attributed to the observation that F induces an enhancement of the charge transfer between H-2 molecules and the Ca-silicene system. Thus, the Ca-silicene system together with the synergy of F can efficiently facilitate H-2 adsorption-desorption, completing the whole hydrogen storage-release cycle.