Hydrogen storage properties of light transition metal clusters coated on bowl-shaped carbon nanostructures

An interaction between hydrogen molecules and bowl-shaped circumtrindene doped with metal clusters composed of light transition metals (Sc, Ti, and V) is investigated using the density functional theory. Two distinct modes of hydrogen binding are identified, namely Kubas interaction and dissociative binding. When considering the interaction of circumtrindene doped with tetrahedral metal clusters with three hydrogen molecules, dissociative binding is energetically preferred over the Kubas interaction. These systems can bind additional hydrogen molecules via Kubas interactions, with the number of bound hydrogen molecules depending on the transition metal as follows: six in case of Sc-based systems, while only three and four in case of Ti- and V-based systems, respectively. Additional hydrogen molecules can be physisorbed to the studied metal clusters. Metal–hydrogen bond strength, evaluated via the QTAIM analysis, increases in the following order: Sc—H < Ti—H < V—H. In case of hydrogen saturation of the studied systems, corresponding to ten hydrogen molecules, the calculated gravimetric density reaches up to 3.2 wt %.