Theoretical Study On Hydrogen Storage Properties Of Gallium Clusters And Sandwich All-metal Composites

Due to the characteristics of high calorific value,environmental protection,abundant source and high combustion efficiency,hydrogen is considered to be a kind of clean energy with great potential for development.At present,the main bottleneck encountered in the development of hydrogen energy is the lack of safe and efficient hydrogen storage materials.The traditional hydrogen storage methods is generally based onpurely physical or chemical adsorption,however,these hydrogen storage methods usually require a lower temperature orhigher pressure,so that there are many problems in the course of their applications,such as high energy consumption,low reserves,insecurity and so on.Metal cluster has received extensive attentions of the researchers owing to its stable structure,high hydrogen storage density,reversibleabsorption and desorption of large amount of hydrogen,and suitable for extensiviy storage and transportation of hydrogen.As an ideal hydrogen storage material,the binding energy of hydrogen and metal clusters should be in the range of 0.1?0.6 eV,so that hydrogen can be adsorbed and desorbed under near ambient conditionsin reversible way.In this paper,the structures and hydrogen storage properties of Gan and Gan-1Mg(n=2-12)clusters were designed and studied based on density functional theory.The research results are as follows:(1)The Gan(n=7-12)clusters are formed by adding the Ga atoms on the basis of the Ga6 configuration.Gan-Mg(n=2-12)clusters are formed by substituting one Ga atom in the Gan cluster by Mg atoms.The structure of Gan-1Mg cluster is similar to the Gan cluster,in which Mg atoms are far away from the main clusters Gan-1;The structure of Ga3Mg and Ga4Mg clusters is different from Ga4 and Gas.The average binding energy analysis shows that the stability of Gan and Gan-1Mg metal clusters increases with the n value increasing.Gan-1Mg clusters are available in two separate forms,one for the separation of a Mg atom from the cluster;the other for separating a Ga atom from the cluster,where the former is more likely to occur.The dissociation energies analysis shows that the stability of Gan and Gan-1Mg(n=3,5,7,10)clusters was higher than that of other clusters.(2)Hydrogen can be adsorbed on the cluster in the form of whole molecular or atomic.The results of the dissociation energies and the second-order difference of energy indicate that GanH2(n=4,7)and Gan-1MgH2(n=3,7,9)clusters are more stable than others.The HOMO-LUMO gap analysis shows that GanH2(n=4,7,9,11)and Gan-1MgH2(n=3,7,9,11)are more stable than other clusters.In conclusion,the stability of GanH2(n=4,7)and Gan-1MgH2(n=3,7,9)is higher than that of other clusters.(3)The stability of clusters before and after hydrogen absorption analysis shows that the stability of Ga7?Ga2Mg and Ga6Mg is higher than that of the other clusters.The binding energies of Ga7 and Ga6Mg clusters with hydrogen are in the range of 0.1?0.6 eV,so that it is expected as a potential hydrogen storage material.In addition,the aromaticity and stability of the sandwich-type all-metal complex Al8TM2(TM = Sc,Y,La,Ti,Zr,Hf,V,Nb,Ta)are studied.On this basis,the hydrogen storage properties of the complex Al4Sc2Al4 are also discussed.The research results are as follows:(1)The two transition metal atoms TM(TM=Sc,Y,La,Ti,Zr,Hf,V,Nb,Ta)can be inserted into two Al42-ligands to form a stable sandwich-type all-metal complex Al8TM2,and the Al42-ligand in the complex still maintains the ?a and ? aromaticity.(2)Al4Sc2Al4 complex bonded with hydrogen through the multi-center bond,which can be identified by a specific frequency.The processes of Al4Sc2Al4 system absorption and desorptionwith hydrogen will be tuable,when induced by infrared spectrum of specific vibration.