H2 ADSORPTION AND STORAGE ON Ni4 CLUSTER EMBEDDED IN MULTIVACANCY DEFECTED GRAPHENE. A DFT AND THERMODYNAMIC STUDY

AMBRUSI, R.E.; MORELLI, G. A.; ORAZI, V.; MARCHETTI, J.M.; JUAN, A.; PRONSATO, M.E.

Workshop; IX Workshop on Novel Methods for Electronic Structure Calculations; 2021

Carbon materials such as graphene can efficiently storage hydrogen only at cryogenic temperatures since hydrogen molecules weakly physisorb on the surface [1]. Decorating graphene with transition metals trapped by defects increases considerably the storage capacity reinforcing the bonding and also by the spillover process [2,3]. In the present work, Hydrogen adsorption stability, geometry, electronic structure and mechanism has been investigated on Ni4 cluster embedded in graphene with three, four and six vacancies by density functional theory (DFT) calculations. An energetic analysis of hydrogen adsorption by addition of one to four H2 molecules was performed for each system in order to determine their hydrogen storage capacity. Dispersion force contribution to the adsorption energy is quantitative evaluated to know whether H2 molecules adsorption behavior is dominated by chemical or van der Waals interactions. A further analysis of this type of interactions is also addressed by total and partial density of states. Bonding and charge transfer characteristics for the different steps involved in the adsorption mechanism are also included. Special attention is given to the effects caused by this new Ni/graphene interface to the hydrogen adsorption behavior. Besides, the Gibbs free energy change with temperature was obtained according to statistical mechanics through a canonical ensemble approach.