Visualizing Electrochemical Oxidation and Dissolution of Platinum Surfaces at the Atomic Scale

The durability of platinum (Pt) electrocatalysts in electrochemical energy conversion is fundamentally challenged by surface oxidation and dissolution during electrochemical operation. Although Pt surface oxidation has commonly been discussed in terms of a "place exchange" mechanism between Pt and oxygen, atomic-scale insight into its potential-dependent progression has remained limited. Herein, we directly visualize atomic electrooxidation and dissolution of {111}-terminated surfaces of octahedral Pt nanoparticles by employing ex situ differential-phase-contrast scanning transmission electron microscopy combined with online inductively coupled-plasma mass spectroscopy and density functional theory calculations. We reveal the atomistic structural evolution of the {111} nanoparticle surface with progressively increasing electrode potentials (0.8-1.5 V), from the initial lattice expansion induced by adsorbed oxygen, to vacancy-induced formation of two-dimensional, lattice-contracted PtO_x monolayers, and finally to a dimensional transition to three-dimensional PtO₂ growth. Furthermore, we demonstrate how the potential cycling protocols (triangular versus square wave cycling) decisively control the final oxide's dimensionality (multilayer versus single layer) and stability. These atomic-scale insights establish how electrochemical conditions dictate Pt oxidation pathways and atomistic structural evolution, providing a mechanistic basis for understanding and improving the durability of Pt-based electrocatalysts.