<i>In Situ</i> Observation of Active Surface Etching in Gold Nanoplates: Evidence for Intermediate Ligand Effects

We report the in situ observation of active surface etching in Au nanoplates using liquid-cell TEM. By analyzing the distinctive etching modes and in combination with our previous ex situ etching studies, we infer and substantiate the mysterious ligand behaviors: (1) the ligand plays dominant roles in etching, and its passivation is neither static nor uniform; (2) the ligand-deficient active sites and ligand-rich passivated sites are gradually and dynamically developed; and (3) the wavelike behavior of the etched nanoplate edges highlights the critical role of the dynamic diffusion of reactants. Comparisons among different thiol-based ligands confirm the generality of these conclusions. Finally, we integrate our hypotheses on the effects of ligands and reactant diffusion in kinetic Monte Carlo simulations. The fact that the main experimental trends are reproduced in silico strongly supports the proposed mechanisms of active surface etching.