First-Principles Study On The High Activity Cu@Pt Core-shell Nanocatalysts For Oxygen Reduction

Nowadays, fuel cells are receiving more and more attention. Among of the different fuel cells,Polymer Electrolyte Membrane Fuel Cells （PEMFCs） are one of the promising candidates for energyconversion applications. Traditionally the electrodes catalyst is the Pt/C. For the widespread usage ofPEMFCs, there are still some problems needed to be solved. For example, Pt is the precious metal whichmakes the cost of PEMFCs too high. Moreover, the oxygen reduction reaction （ORR） on cathode is sloweras compared with hydrogen oxidizing reaction （HOR） on anode which causes the energy lost up to30%.Novel catalysts with higher ORR activity therefore need to be developed. Core-shell nanoparticle catalystshave been studied greatly because of their high surface-to-volume ratios, high stability and high catalyticactivity.In this thesis, the first-principles methods based on the density functional theory are used toinvestigate the stability and catalytic activity of the Ih Cu@Pt core-shell particles. The work performed andresults reached are as follows:1) Through studying the geometric and electronic structures of the Ih Cu@Pt12cluster, it is found thatsubstituting of the Pt atom in the core of the symmetric Pt13clusters with a Cu atom could enhance thestability of the Ih Pt13structure. The resulted Ih Cu@Pt12is the most stable structure with the highestaverage binding energy among the three symmetric Cu@Pt12core-shell isomers. And uponexchanging the Cu in the core with one of the Pt atoms in the shell, the average binding energy islowered, indicating that the Cu atom prefers to be in the core. The Ih Cu@Pt12cluster thus possessesthe highest stability.2) On the Ih Cu@Pt12, two adsorption configurations （t-b-t and t-h-b） are obtained for O₂. It is found thatthe t-b-t configuration is more stable, and the t-h-b configuration can easily rotate to the t-b-tconfiguration with a very low barrier. Then the dissociation process of O₂on t-b-t site is studied. Thedissociation barrier of O₂on the Ih Cu@Pt12is lower than that on the Pt（111）, indicating that the IhCu@Pt12is benefit for the dissociation of O₂.3) There are three stable adsorption sites for O on the Ih Cu@Pt12: top, bridge, hcp. It is found that the adsorption on the hcp site is the strongest. Therefore, the O atom tends to be adsorbed on the moststable hcp site. By studying the diffusion of O atom on these three sites, it is concluded that the major（or easy） diffusion path would be the ‘bridge-hcp-bridge-hcp-…’, and the maximum diffusion barrier islower than that on the Pt（111）.Since the dissociation of O2and diffusion of atom O are the rate determinant elementary steps forORR, our calculated results demonstrate the much higher ORR activity of the Ih Cu@Pt12core-shellnanoparticle, indicating that the Ih Cu@Pt12nanoparticle is a good candidate as the ORR catalyst.