Electric field induced reversible switch in hydrogen storage based on single-layer and bilayer graphenes

In an ideal hydrogen storage system, binding strength should increase during adsorption whereas the opposite should be the case during desorption. These two seemingly contradictory requirements limit the types of systems that can be utilized. Density-functional theory (DFT) calculations are carried out to investigate hydrogen physisorption on Li-doped single-layer and bilayer graphenes. We propose that the superimposition of an electric field can be used to effectively control hydrogen adsorption. More specifically, we report that hydrogen binding can be enhanced under a positive electric field, whereas it can be weakened under a negative electric field. Our results show that the binding strength increases by 88% when a field with a magnitude of +0.020 au is imposed. Hirshfeld charge analysis results suggest that an increase in the binding strength will occur as long as the Li (or C) carries more positive (or negative) charges. Our calculations demonstrate that, in the case of Li-doped graphene, the application of a positive electric field yields an increase in binding strength during adsorption while a negative field decreases the binding strength during desorption.