Potential hydrogen storage materials from metal decorated 2D-C2N: an ab initio study

Abstract

Two dimensional nitrogenated holey graphene (2D-C₂N) is often considered as an ideal material for hydrogen storage applications owing to its lower mass density and high surface-to-volume ratio. As the interaction between H₂ and pristine 2D-C₂N is very weak with an adsorption energy of only 0.10 eV per H₂, it is important to improve it through appropriate materials design. Using density functional theory calculations, we investigated the hydrogen storage properties of metal (M = Mg, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, and Zn) decorated 2D-C₂N. From this study, we found that M binding energy on 2D-C₂N is greater than the cohesive energy of the respective bulk metals, indicating that the metal is strongly bonded with the 2D-C₂N, which rules out the metal clustering issue. In particular, 2D-C₂N with Mg decoration leads to 6.79 wt% hydrogen storage capacity with a desirable adsorption energy which is above the Department of Energy's target. The electronic structure analyses show that the Mg decoration leads to a semiconductor-to-metallic transition in 2D-C₂N. Our chemical bonding analyses through partial density of states, charge density, electron localization function, charge transfer, and Bader effective charge confirm the presence of an iono-covalent character for Mg decorated 2D-C₂N. This indicates that the H₂ molecules are adsorbed by a polarization mechanism. Overall, our results suggest that Mg decorated 2D-C₂N is a promising candidate for potential hydrogen storage applications.