Ti-decorated C30 as a high-capacity hydrogen storage material: insights from density functional theory

Abstract

Employing density functional theory, we explore the hydrogen storage proficiency of titanium-decorated fullerene C₃₀, an allotrope of carbon that comprises pentagonal and hexagonal rings. Titanium is bonded strongly on the hexagonal ring of C₃₀ with a binding energy of −3.48 eV due to charge transfer from the Ti 3d orbital to the C 2p orbital of C₃₀. A single C₃₀ could hold 4 Ti atoms, where each Ti atom can hold 5 molecules of H₂ reversibly, with an average adsorption energy of −0.50 eV and average desorption temperature of 368 K leading to a storage capacity of 6.76 wt%, higher than the target set by the US D.o.E. As per Bader charge portioning, 1.52e charge gets transferred from Ti to C₃₀ which is responsible for strong bonding of Ti. The interplay between Ti and hydrogen is explained through Kuba's interaction which is defined as a charge donation from σ orbitals of hydrogen to the vacant 3d orbital of Ti and a subsequent back transfer of charges from the filled 3d orbital of Ti to the σ* orbital of hydrogen. The structural integrity of the system remained intact at room temperature as verified through ab initio molecular dynamics simulations, and the presence of a metal diffusion barrier of −2.75 eV can prevent metal–metal clustering. The aforementioned features of the material infer that Ti-decorated C₃₀ is a stable, practically viable, 100% recyclable, and efficient hydrogen storage system.