Electrochemical Degradation of Pt-Ni Nanocatalysts: An Identical Location Aberration-Corrected Scanning Transmission Electron Microscopy Study.

The evolution of Pt-Ni nanoparticles supported on amorphous carbon is investigated before and after electrochemical potential cycling (0.6-1.1 V), using aberration-corrected scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS). During voltage cycling and due to the dissolution of  nanoparticles, single ions/atoms and ionic/atomic clusters emerge and diffuse across the carbon support toward larger nanoparticles, where they redeposit. We observe that the preferred locations for the dissolution are the steps and corners of the nanoparticles. On the other hand, the redeposition process happens often on {111} type planes. In addition, contrary to the conventional view, where larger particles grow isotropically from smaller ones, this research work shows that anisotropic growth of smaller particles occurs during potential cycling. The reason for this behavior seems to be related to the fact that smaller particles with thicker Pt-rich shells trigger the nucleation and deposition of Pt.