Zr doped C24 fullerene as efficient hydrogen storage material: insights from DFT simulations

Abstract

In this article, we report the hydrogen storage capacity of zirconium (Zr) decorated C24 fullerene using state-of-the-art density functional theory simulations. Our study shows that zirconium, like most other transition metals, tends to bind strongly on the C–C bridge of C24 fullerene with a maximum binding energy of −3.64 eV. Each Zr atom decorated over C24 fullerene can adsorb a maximum of 7H2 molecules with an average adsorption energy of −0.51 eV/H2, leading to a gravimetric density of 7.9 wt%, which is higher than the prescribed target of 6.5 wt% set by United States-Department of Energy. There is a charge transfer from Zr to C atoms in C24 fullerene, which is the primary cause of the binding of Zr with C24 fullerene. H2 molecules are adsorbed over Zr sorption sites via Kubas-type interactions, which include charge donation from the filled s orbitals of hydrogen to the vacant 4d orbital of Zr and subsequent back charge donation to unfilled s* orbital of hydrogen from the filled 4d orbital of Zr. The structural stability of the Zr + C24 system at a high temperature of 500 K is verified using ab-initio molecular dynamics calculations. The high diffusion energy barrier of Zr (2.33 eV) inhibits clustering between the Zr atoms decorated on the C24 fullerene and ensures the system’s practical feasibility as a high-capacity H2 adsorbing system. Therefore, our computational studies confirm that Zr decorated C24 fullerene is stable and can be regarded as a potential candidate for H2 storage systems with optimum adsorption energy range.