A Study Of Hydrogen Adsorption Induced Structures And Properties Of Bimetallic Pt-Pd Nanoclusters

Bimetallic nanoclusters show excellent hydrogen adsorption properties in the recent years,provide a novel solution to the storage of hydrogen energy.Here we analyzed the structural and electronic properties of bimetallic PtnPd55-n(n = 0,9,11,13,14,18,27,37,41,42,44,46,55)nanoclusters based on the density functional theory,and calculated the effect of hydrogen adsorption on the structures and properties of those cluster,and investigated the interactions between hydrogen and metal in clusters.The ground state structures of PtnPd55-n bimetallic nanoclusters were found to be icosahedron through a global minimum search using minima hopping method based on the EAM potential,Pt and Pd atoms are randomly mixed in the clusters.The atoms have a tendency to segregation when the number of Pt atoms in the cluster is less than 37,Pt atoms tend to occupy the core sites while Pd atoms tend to occupy the surface site.The atomic composition has an influence on the stability of a cluster,according to the results of excess energy calculation,Pt13Pd42 nanocluster is the most stable cluster among all the randomly mixed clusters.The excess energy and the average DDEC charge of all Pd atoms are positively correlated,the less amount of charge transfer from Pd atoms,the more negative the excess energy will be,and that means the more stable the cluster will be.PtnPd55-n nanoclusters have excellent hydrogen storage abilities,the calculation of hydrogenation energies shows that the system is stable even when we add 80 hydrogen atoms to it.Most of the hydrogen atoms are adsorbed on the surface of the clusters,while part of the hydrogen atoms are penetrated into the inside of the clusters,increasing the amount of adsorbed hydrogen will lead to the lattice expansion of the cluster.Structural distortion will occur when a large amount of hydrogen atoms are adsorbed by the cluster,and the hydrogen induced distortion will be more easily to occur with the increasing of Pt concentration.Hydrogen prefers to form a two-coordinate structure with Pt ligand,while tends to form a three-coordinate structure with Pd ligand.The preferential site for hydrogen adsorption on the surface of a cluster is hollow site when the surface are composed mostly by Pd atoms,but when adsorbing on a Pt-rich surface,that preferential site should be bridge site.DDEC charge analysis shows the electrons are transferred from Pt and Pd atoms to hydrogen,and the amount of charge transfer from Pd to hydrogen are larger.Induced by the hydrogen adsorption,hybridized states are formed in the low-energy region of metal states,then bonded with hydrogen atoms to increase the stability of adsorption.