Hydrogen adsorption behavior on AXenes Na2N and K2N: a first-principles study

It is a consensus that the hydrogen economy has come to a standstill due to the lack of feasible hydrogen storage solutions, especially, the suitable hydrogen storage materials. In this work, the potential of a new kind of two-dimensional (2D) AXenes, Na2N and K2N, as hydrogen storage materials are evaluated by the first-principles calculations. In particular, we find that Na2N in T phase indicates a hydrogen storage capacity as high as 6.25 wt% with a desirable hydrogen adsorption energy of -0.167 eV per H-2 molecule and a desorption temperature of 216 K, identifying T-phase Na2N to be a very promising reversible hydrogen storage material. In accordance to our results, H-2-Na2N interaction causes H-2 charge polarization, which is responsible for the moderate binding strength. In addition, Gibbs adsorption free energy reveals that the system will be more stable as more H-2 molecules are loaded on the surface.