First-principles calculation identification of ultrahigh hydrogen storage capacity in g-Mg3N2

Abstract

Due to intrinsically existing uniform periodic vacancies (hollow) and light metal ions (Mg2+), the two-dimensional (2D) g-Mg3N2 is identified as a promising candidate material for hydrogen storage from first principles calculations. The hydrogen storage mechanism is carefully analyzed through the electronic structure change of the g-Mg3N2 substrate before and after hydrogen molecule absorption. Ultrahigh hydrogen storage gravimetric density and surface area of 15.2% and 7.9 * 10−8 kg/m2 is predicted for the g-Mg3N2, without additional alkali metal decorations. The appropriate sequential adsorption energy ranging from − 0.139 to − 0.078 eV and the average adsorption energy of −0.103 eV/H2 ensures hydrogen storage has very good reversibility. Ab initio molecular dynamics simulations show that a large percentage of the hydrogen molecules can be released from the g-Mg3N2 host at elevated temperatures, indicating that the efficiency of hydrogen storage and release can be very high. Meanwhile, the g-Mg3N2 lattice is very stable upon hydrogen adsorption, showing very good cycling performance in practical applications. Benefit from the large holes in the structure of g-Mg3N2, hydrogen molecules can move easily from one side of the g-Mg3N2 plane to the other through the holes (with only 96 meV barrier height), which is also beneficial to increase the hydrogen storage efficiency.