H<inf>2</inf> adsorption by noble gas insertion compounds: A computational study

In order to find a solution of energy-related problems, sophisticated hydrogen storing materials are needed as hydrogen is an abundant and environment friendly fuel. We have investigated the hydrogen storage potential of Ng inserted metal acetylide and metal cyanide compounds (metal ​= ​Cu, Ag and Au) at the ωB97X-D/cc-pVTZ-PP level of theory. Due to the difference in electronegativity and formal charge on metal atoms in the insertion compounds, the interaction with the hydrogen molecule is expected to be different. The adsorption energies, the free energy of adsorption, natural charges on atomic centers/moieties are obtained through the natural population analysis, and energy decomposition analysis has also been carried out for nH2···MNgCCH and nH2···MNgCN (n ​= ​1–3). The hydrogen adsorption capacity of the strongest and the weakest cases has also been investigated. Both the insertion compounds, MNgCCH and MNgCN, are found to adsorb a maximum of three hydrogen molecules on the metal site. The single H2 adsorbed minimum energy structures of studied compounds show a “T-shaped” orientation while double H2 adsorbed minimum energy structures are of “Y- shaped” geometry and those of tricoordinated structures resemble “Td-like” shape. The negative value of Gibbs free energy change suggests the thermodynamical spontaneity of the hydrogen adsorption process.