First Principles Study On Dynamics And Thermodynamics Process Of Platinum-based Metal Clusters In Service

The development and application of fuel cell technology can alleviate the dependence of human beings on fossil energy,but it is restricted how to design high activity,low cost and high durability fuel cell catalyst.With the rapid development of nanotechnology,binary and ternary platinum-based nanocatalysts can be prepared by alloyed with platinum and transition metal.This reduces the use of platinum and improves the activity of the catalyst by surface regulation.This kind of atomic level regulation can not only change the electronic structure of platinum atoms on the surface,but also reduce the activation energy of reaction through synergetic effect.These efforts will break a barrier for the development of fuel cell technology.In this paper,the first principles method based on density functional theory(DFT)is used to study the reaction kinetics of platinum-based metal cluster catalysts and the thermodynamic process of their degradation and deactivation in acidic media.The main research work is as follows:(1)FePt bimetallic cluster catalysts can efficiently catalyze the CO oxidation reaction,and different Fe/Pt chemical ratios have different catalytic activities.In this part,the size effect and chemical ratio effect of FePt bimetallic nanocatalyst were obtained by improving the reaction kinetics model and studying the reaction kinetics process.The optimized chemical ratio and size of FePt bimetallic nanocatalyst with the highest catalytic activity were found.(2)Platinum-based bimetallic core-shell nanocatalysts will inevitably be corroded in acidic media,and their special structures will be destroyed,thus losing their activity.In the thermodynamic process of corrosion dissolution,galvanic corrosion and pitting corrosion work together.Through the calculation of this part,the change of dissolution potentials of 12 species M@Pt core-shell metal clusters in corrosion thermodynamic process was studied,and the micro mechanism of galvanic corrosion and pitting corrosion was obtained.It has important theoretical value for understanding the thermodynamic process of deactivation of platinum-based bimetallic core-shell nanocatalysts.(3)In order to prolong the service life of platinum-based metal core-shell structure nanocatalyst,adding migration barrier layer or protective layer in the catalyst can effectively delay the occurrence of pitting corrosion.In this part,a Cu/Os/Pt sandwich structure nanocatalyst was constructed by adding an Os atom layer into the Cu@Pt bimetallic core-shell structure nanocatalyst.The kinetics and thermodynamics process of Cu segregation and the vacancy migration under the conditions of point defect and oxygen adsorption are studied.The micro mechanism of Cu segregation and Os inhibiting Cu segregation is summarized.