Hydrogen adsorption and dissociation on the TM-doped (TM=Ti, Nb) Mg55 nanoclusters: A DFT study

Abstract

The slow hydrogenation kinetics and high reaction temperature of Mg primarily limit its application for mobile hydrogen storage. H2 adsorption and dissociation on the pure and TM-doped (TM = Ti, Nb) Mg55 nanoclusters are systematically studied by using density functional theory (DFT) calculations. It is found that the introduction of Ti and Nb atoms into Mg55 nanocluster can greatly modify the electronic structure of Mg55 nanocluster and enhance the stability of system. Through the analyses of results from the climbing image nudged elastic band (CI-NEB) and reaction rate constant, we also find that the energy barriers of H2 dissociation on TM-doped Mg55 nanoclusters can be significantly decreased due to the addition of Ti and Nb. Adding Ti and Nb atoms can dramatically improve the rate constant of H2 dissociation, especially for H2 dissociation on Mg54TM2 (TM atom replacing the inner shell position), Mg54TM3 (TM atom replacing the outermost vertex) and Mg54TM4 (TM atom replacing the outermost edge position) nanoclusters. Moreover, compared with the Ti dopant, the Nb will generate a lower activation barrier for H2 dissociation on TM-doped Mg55 nanoclusters. We also suggest that the subsurface and surface positions (Mg54TM2, Mg54TM3, Mg54TM4) are the ideal substitutional sites for TMs.