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 C 24 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 C 24 fullerene with a maximum binding energy of −3.64 eV. Each Zr atom decorated over C 24 fullerene can adsorb a maximum of 7H 2 molecules with an average adsorption energy of −0.51 eV/H 2 , 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 C 24 fullerene, which is the primary cause of the binding of Zr with C 24 fullerene. H 2 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 4 d orbital of Zr and subsequent back charge donation to unfilled s * orbital of hydrogen from the filled 4 d orbital of Zr. The structural stability of the Zr + C 24 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 C 24 fullerene and ensures the system’s practical feasibility as a high-capacity H 2 adsorbing system. Therefore, our computational studies confirm that Zr decorated C 24 fullerene is stable and can be regarded as a potential candidate for H 2 storage systems with optimum adsorption energy range.