Using the first-principles method based on density functional theory,we study the hydrogen storage properties of Li-doped single-layer aluminum nitride nanostructures (AlN).For the pristine AlN sheet,each Al atom adsorbs one H2 with an average binding energy of 0.14 eV/H2.The hydrogen binding energies and storage capacities can be markedly increased by doping Li atoms onto the AlN sheet.The charge analysis shows that there are charges transferring from the Li atoms to the AlN sheet,thus the charged Li atoms can polarize hydrogen molecules and enhance the interaction between hydrogen molecules and the AlN sheet.In the fully loaded cases,the Li-doped AlN sheet can contain up to 8.25wt％ of molecular hydrogen with an average binding energy of 0.20eV/H2.Hydrogen has long been considered as a carbondioxide-free energy carrier of the future.[1-3] One of the primary barriers preventing the large-scale use of hydrogen is the lack of an economic,effective and safe hydrogen storage medium.To achieve eventual economic feasibility,the materials should store hydrogen with large gravimetric and volumetric densities and operate under ambient thermodynamic conditions.[4]To meet these criteria,hydrogen storage media should only be considered among systems composed of light elements and its adsorption energy for H2 should be in the range of 0.1-0.2 eV/H2.[5]