2020 Volume 84 Issue 7 Pages 244-252
The surface morphological change of electro-deposited Pt–75 at％ Cu (Pt–75Cu) nanoparticles under potential cycling were investigated by identical-location scanning electron microscopy. Electro-deposited nanoparticles consisted of numerous nuclei (～3 nm in diameter) that agglomerated to form larger secondary particles (30-50 nm). In the initial immersion in the sulfuric acid, Pt-shell formed on the surface due to the selective dissolution of Cu from Pt-75Cu. Although around 40％ of Cu dissolved, noticeable surface morphological change does not appear. Then Pt-75Cu was subjected to potential cycling between 0.05-1.0 V, surface smoothing of the nanoparticles slightly progressed due to surface diffusion of Pt. On the other hand, when Pt-75Cu was potential-cycled between 0.05-1.4 V, a particle diameter of the nanoparticles drastically decreased, and the nucleus on the surface completely disappeared owing to Pt dissolution and re-deposition. The heat-treated nanoparticles formed numerous pores on the surface during the immersion and the initial stage of the potential cycle. However, the final morphology was similar to the non-heated one. The formation of pores can be explained by the coarsening of nuclei by heat treatment.
