  In this work, we investigate the hydrogen-storage properties of Zr-decorated
$\gamma$-graphyne monolayer employing Density Functional Theory (DFT) for green
energy storage. We predict that each Zr atom decorated on graphyne sheet (2D)
can adsorb up to seven H$_2$ molecules with an average adsorption energy of
-0.44 eV/H$_2$, leading to a hydrogen gravimetric density of 7.95 wt%, and
desorption temperature of 574 K, particularly suited to fuel-cell applications.
Decorated Zr atom strongly attached to graphyne due to charge transfer from Zr
to graphyne sheet. Hydrogen molecules adsorb on Zr decorated graphyne with
Kubas type of interaction. The 4.05 eV diffusion energy barrier between Zr
decorated position, and its neighboring pores may avoid the metal-metal (Zr-Zr)
clustering. The stability of Zr+$\gamma$-graphyne is confirmed by performing
ab-initio molecular dynamics simulations at room temperature and at estimated
average desorption temperature. Hence, our calculations show Zr functionalized
on $\gamma$-graphyne could be a promising solid-state hydrogen storage
material.
