First Principles Computational Study On The Catalytic Performance Of Cu/Au Doped Pt Nanocrystals For Oxygen Reduction Reaction

Since the industrial revolution,the consumption of fossil energy on the earth has led to an increase in greenhouse gases in the atmosphere,and the development and utilization of new energy has attracted many attentions.Proton exchange membrane fuel cells have the advantages of cleanliness and sustainable development and are one of the methods to solve the energy crisis.However,the slow kinetics of the oxygen reduction reaction(ORR)occurring on the cathode surface and the poor stability of the cathode itself limit the industrialization of fuel cells.Therefore,it is important to find a high performance,high stability,and low cost cathode electrocatalyst.Compared with the widely used commercial platinum(Pt)carbon catalysts at present,Pt-based nanostructures with high specific surface area usually exhibit excellent ORR activity,and become the focus of research and development of high performance cathode electrocatalyst.Based on the problems faced by cathodic electrocatalysts,we designed Pt-based nanoparticle materials and studied their catalytic properties and electrochemical stability with the density functional theory(DFT).The main contents are as follows.The surface structure and ORR activity of Cu-doped,truncated octahedral,Pt nanoparticles were studied by DFT.The calculation results show that the strain effect caused by surface defects makes the oxygen adsorption capacity at the surface sites of Pt nanoparticle too strong,while the doping of Cu component can weaken the oxygen adsorption energy of Pt skin that becomes the most active when Cu replaces only the subsurface layer of Pt nanoparticles.Based on above results,combined with the d-band center theory,the quantitative relationship between the general coordination number and strain or d-band center or oxygen adsorption energy is established for the surface sites of different coordination and strain environments,and thus suitable oxygen adsorption energy can be screened.These findings provide theoretical guidance for the experimental design of high-efficiency Pt-based nanoparticle catalysts by composition-or surface-engineering.The electrochemical stability of undecorated or gold-decorated,truncated octahedral,Pt nanoparticles was studied by DFT.The calculation results show that the electrochemical stability of pure Pt nanoparticles is poor due to highly unsaturated vertex and edge atoms on surface.After modifying the surface with Au,it is found that Au atoms are not easy to form alloys with Pt in the bulk or core,but preferentially occupy the vertice,edges and(100)facets,forming a thermodynamic stable nanostructure.Furtermore,the electrochemical stability of Pt nanoparticle can be globally promoted if it is decorated by a complete Au nanoframe,without reducing its catalytic activity due to largely exposed Pt(111)facets.Therefore,small amount of Au can be used to modify the surface of Pt nanoparticles to obtain good thermodynamical and electrochemical stability,without reducing the catalytic activity.