An ab initio study of reversible dihydrogen adsorption in metal decorated γ-graphyne

Abstract

We present the detailed comparative study of dihydrogen adsorption in Li, Mg, Ca, and Sc decorated γ-graphyne (Gγ ) performed with density functional theory calculations. Hydrogen molecules are sequentially loaded onto metal decorated Gγ . Maximum hydrogen weight percentage for Li, Mg, Ca, and Sc decorated Gγ is found to be 8.69, 7.73, 8.10, and 6.83, respectively, with maximum 8 H2 on Li, Mg, and Sc while 10 on Ca decorated Gγ . All hydrogen molecules are physisorbed over all the complexes except that the first one on each Sc of Gγ - 2Sc is chemisorbed. Orbital hybridization involved in Dewar coordination of metal decoration and the Kubas mechanism of hydrogen adsorption has been explained with the partial density of states. Lower values of adsorption and desorption energies in these complexes indicate the reversibility of adsorption. These complexes obey high hardness and low electrophilicity principles and contain no imaginary frequencies which specify their stability. In Born-Oppenheimer molecular dynamics, reversibility of adsorption is proven at various temperatures. Based on the comparative studies of hydrogen weight percentage, energetics, stability, and reversibility, Gγ -2Ca is proven to be a better hydrogen storage candidate. This comprehensive study confirms the potential of metal decorated γ-graphyne as a suitable hydrogen storage material.