Hydrogen adsorption on alkali metal decorated blue phosphorene nanosheets

Abstract

Hydrogen storage capabilities of blue phosphorene nanosheet, decorated with lithium and sodium atoms were systematically studied using ab-initio Density Functional (DFT) calculations. Hydrogen molecule adsorbs on pristine blue phosphorene with an adsorption energy of 0.06 eV, which is much lower than the threshold energy of ∼0.10 eV required for practical applications. When blue phosphorene is decorated with lithium or sodium atoms on its surface, hydrogen adsorption energies are drastically increased to 0.25 eV and 0.18 eV respectively. It is found that a lithium atom adsorbs up to three and sodium atom up to four hydrogen molecules. Analysis of density of states and difference charge density calculations confirm the hybridization of hydrogen and lithium states. Coverage studies show a gravimetric storage capacity for hydrogen to be 5.5% on lithium decorated blue phosphorene, which is better than that of lithium decorated black phosphorene (4.4%).