First principle study of reversible hydrogen storage in Sc grafted Calix[4]arene and Octamethylcalix[4]arene

Abstract The use of hydrogen as a sustainable clean energy source has several benefits, such as reduction in dependency on petroleum fuel and emission of green house gases, and enhanced energy security. The H2 storage properties of Sc grafted calix[4]arene (CX) and octamethylcalix[4]arene (MCX) are investigated by using density functional theory with M06/6-311G(d,p) level of theory. It is observed that Sc strongly binds with benzene rings of CX and MCX through Dewar coordination with average Sc binding energy of 1.09 and 1.25 eV, respectively for CXSc4 and MCXSc4. Each Sc atom adsorbs 4 H2 molecules on both the Sc grafted systems and H2 molecules are bound by Kubas interaction with H2 interaction energy in the range of 0.2–0.5 eV. The calculated conceptual reactivity index shows the stability of the systems increases with number of hydrogen molecules. Hirshfeld charge analysis shows the charge transfer mechanism during H2 adsorption. Born-Oppenheimer molecular dynamics simulations of CXSc4-16H2 and MCXSc4-16H2 systems, show that these systems are stable up to 273 K and all the adsorbed H2 releases at 373 K. The hydrogen storage capacity of Sc grafted CX system is found to be 8.9 wt % and for MCX system is 9.7 wt %. The energy and storage capacity meets the US Department of Energy target, which makes them a propitious hydrogen storage material.