Surface Modulation Of Pt-Based Nanoparticles Induced By Electrochemical Adsorption-Desorption

The nature of catalytic reactions is reactions on the interface,and the influence of the surface structure of catalysts on the catalytic kinetics is particularly important.The surface structure of catalysts often undergoes some changes under the atmosphere or heating conditions contained in the use environment.Deeply understanding the evolution of the surface structure of catalysts in various environments is of great significance to guide the design of a reasonable catalyst structure.Currently carbon-loaded Pt nanoparticle catalysts are the most widely used electrocatalysts and have been widely used in proton exchange membrane fuel cells.The proton exchange membrane fuel cell contains a complex electrochemical environment,and the change of the surface structure of the Pt nanoparticle catalyst during its work needs to be studied.In this thesis,firstly,the electrochemical adsorption and desorption reversibility of H/OH on the surface of bulk polycrystalline Pt was investigated by means of electrochemical tests.It was reported for the first time that an unstable peak in the CV curve of Pt catalyst appeared at 0.6-0.8 V after long-term underpotential absorption and desorption of H.Subsequently,the surface structure evolution of pure Pt/C nanoparticle catalysts induced by adsorption/desorption of H/OH was studied.By high resolution transmission electron microscopy,it was found that after a long-term underpotential absorption and desorption of H,the shape of the particles was elongated,showing that the surface represented less {100},more {110},and the ORR performance of the catalyst improved significantly.The adsorption and desorption of OH on the surface of Pt nanoparticles disturbs the structure of the Pt{111} surfaces and forms many {110} steps.After that,the effect of H/OH adsorption and desorption on the surface structure of Pt Ni3 alloy nanoparticles was studied.It was found that induced by prolonged absorption and desorption of H,particles would join nanorods with {100} planes,and the distribution of Pt and Ni in the rods changed.The single Pt shell Ni core nanoparticles formed nanorods penetrated by Ni core.In addition,the stability of nanocatalysts treated by H adsorption and desorption would be greatly improved.Our results indicate that the underpotential hydrogen adsorption and desorption on Pt surface,which is widely used for evaluating electrochemical surface area of Pt catalysts,may itself change the surface structure and catalytic performance of Pt nanocatalysts under long-term cycling.Finally,we used electron tomography technology to characterize agglomerates of nanoparticles with complex three-dimensional structures,excluding the possibility that particles with special projection shapes were artifacts.At the same time,using electron tomography,we measured the dimensional parameters of Pd Cu nanocages with complex three-dimensional shapes.Electron tomography provides powerful research tools for the deep understanding and reasonable designs of this type of catalyst.