Zirconium decorated 2D holey graphyne for high capacity hydrogen storage: Insights from first principles simulations

The hydrogen storage potential of a 2D analogue of graphyne, holey graphyne (HGY) monolayer decorated with the zirconium adatom is explored by the first-principles study. The Zr adatom exhibits a strong binding affinity on the HGY monolayer with -4.44 eV binding energy through an electronic charge transfer mechanism. Consequently, a localized spatial electrostatic field emerges around the Zr adatom and tends to result in the H2 molecules being adsorbed via the Kubas interaction. This interaction is due to back-and-forth charge transfer between the H-1s orbital and the Zr-4d orbital, resulting in a net charge gain by the H-1s orbital and leading to H-H bond elongation. Furthermore, the high energy barrier for Zr diffusion over the HGY monolayer effectively averts the metal clustering concern. The thermal response of Zr-decorated HGY near room temperature and elevated temperatures is examined via ab-initio molecular dynamics simulations. Each Zr adatom has the capacity to accommodate five hydrogen molecules, exhibiting adsorption energies spanning from -0.24 to -0.45 eV, leading to a notably high hydrogen weight percentage of 7.5, above the DOE's criterion of 5.5 wt%. This study validates the effectiveness of utilizing thermodynamically and energetically stable Zr-decorated HGY an outstanding medium for hydrogen storage.