DFT Study On ORR Activity Of Ternary Core-shell Nm@Pt₁Au_n-m-1（N=Fe,Co,Ni;n=19,38,55,79;m=1,6,13,19） Cluster

The performance of low temperature fuel cells is limited by the slow kinetics of oxygen reduction reaction（ORR）,which needs to be overcome by designing effective catalysts with low cost.Although Pt is the commonly used electrode material,the considerable overpotential and high cost prevent its further commercial development.However,the influence of the electronic properties of the multi-element metal core-shell clusters on the reactivity requires a detailed theoretical analysis.The catalyst structure with high activity,high stability and low cost requires careful search.In this paper,using density functional theory,GGA-PW91-PAW method,a series of ORR catalysts with different sizes（19,38,55,79-atoms）and different chemical compositions are studied for activity and stability.These include:pure metal Pt clusters,Ni_m@M_n-m（M=Pt,Pd,Cu,Au,Ag;n=19,38,55,79;m=1,6,13,19）and N_m@Pt₁Au_n-m-1（N=Fe,Co,Ni）.We systematically studied the energy changes in the ORR reaction process,using overpotential as the descriptor of catalytic activity.The origin of activity differences is explained via structural,charge transfer,and electronic structure analyses.This work consists of the following three parts:1.ORR activity of Pt（111）and Pt_n（n=19,38,55,79）clusters.By comparing the overpotential of ORR reaction on Pt（111）and pure Pt_nclusters,the geometric and electronic properties of Pt_nare different from those of Pt（111）.We found that Pt_nare not rational candidate for ORR which arises from strong binding energy of*OH.2.ORR activity of Ni_m@M_n-m（M=Pt,Pd,Cu,Au,Ag;n=19,38,55,79;m=1,6,13,19）.For same size cluster,compared with the Pt_n,Ni_m@Pt_n-mare favorable candidate catalysts for ORR.The effect of Ni core on the cluster activity are as follows:Introducing Ni core influences the configuration of the catalysts and change the charge transfer between the core and shell.Those reasons decrease the adsorption strength of OH,improving activity of Ni_m@Pt_n-m.3.ORR activity of Ni_m@Pt₁Au_n-m-1.Single Pt atom over Ni_mAu_n-mto form Ni_m@Pt₁Au_n-m-1.This result indicated that single Pt atom substitution over Au shell significantly improves the activity of the core-shell material.The ORR catalytic activity of Ni_m@Pt₁Au_n-m-1is higher than Pt（111）.Ni₆Pt₁Au₃₁has the highest ORR activity.Pt decreases the charge of adsorption site and make a great influence on molecular orbital of*OH and adsorption site atom.Those reasons decrease the adsorption strength of OH,causing higher activity.ORR activity of N_m@Pt₁Au_n-m-1（N=Fe,Co,Ni）.Compared with Pt（111）,N_m@Pt₁Au_n-m-1showing superior electro-catalytic performance for the ORR.4.For stability:Ni_m@Pt₁Au_n-m-1>Ni_m@Au_n-m>Ni_m@Pt_n-m>Pt_n.In conclusion,N_m@Pt₁Au_n-m-1is a popential candidate ORR catalyst with durability,high activity and low cost.