A microscopic view on the electrochemical deposition and dissolution of Au with scanning electrochemical cell microscopy – Part II: potentiostatic dissolution and correlation with in-situ EC-TEM

The electrochemical oxidation of gold nanoparticles (NPs) has been examined in H2SO4 and acidified NaCl by combining multiple techniques including scanning electrochemical cell microscopy (SECCM) and in-situ electrochemical transmission electron microscopy (EC-TEM). Our findings provide novel insights into the intricate oxidation dynamics of Au NPs, which are determined by the interplay between passivation and dissolution. SECCM chronoamperometric measurements in the Cl− containing electrolyte reveal distinct current peak events during the dissolution process. We attribute these events to delayed one-by-one NP dissolution following the rapid breakdown of the passive layer formed during the initial stages of anodic polarization, and exposure of the metallic gold core to Cl− ions. Statistical analysis of these peak events further uncovers relationships between the applied potential and the distribution of the peak descriptors over time. The analysis of the charge consumed during each event indicates that NPs undergo partial dissolution interrupted by rapid re-passivation. As the potential increases, the peak current rises and the duration of the peak events decreases due to intensified dissolution and faster re-passivation. The onset time of the peak events displays a highly stochastic nature. In-situ EC-TEM measurements support these findings by confirming that Au NPs dissolve one-by-one at different time intervals and stages, revealing a core-shell structure during the dissolution process. The shell, which is more resistant, leads to a delayed, particle-by-particle dissolution once it is broken down. Quantification of the EC-TEM video allows recreating an equivalent current-time transient which presents peak events similar to these measured by SECCM. These findings contribute to our understanding of the complex and stochastic behavior of nanoparticle dissolution, which cannot be fully explained by traditional (macro) electrochemistry alone. The combination of SECCM and EC-TEM offers high potential to understand complex nanomaterial degradation pathways, essential for the design of durable electrocatalysts for electrochemical conversion and storage applications.