Interfacial Structure and Energy Determine the Heterogeneity in the Electrochemical Metal Dissolution Activity at Grain Boundary

Grain boundaries are defects present in polycrystalline materials that often possess unique electrochemical activity, including in metal dissolution reactions. The structural origin of the enhanced activity at some grain boundaries is often experimentally elusive because of the ambiguity in attributing the activity to a specific grain boundary due to ensemble averaging. Herein, we experimentally elucidate the structural and energetic effect of grain boundary on metal dissolution reaction by colocalized scanning electrochemical cell microscopy (SECCM) and electron microscopy assisted by focused ion beam (FIB). The local dissolution activity at isolated locations containing only single grain boundaries is measured from SECCM. The structure and orientation of the same grain boundary planes are characterized by electron backscatter diffraction and FIB, which is confirmed by transmission electron microscopy (TEM). The relative interfacial energy of these grain boundaries is also measured via the thermal grooving method. Using anodic dissolution at Ag grain boundaries as a model system, we found that the dissolution rate increases with grain boundary energy and the density of broken bonds at the grain boundary plane. The results explain the heterogeneity in the activity of metal dissolution at different grain boundaries, elucidating the initiation sites of metal dissolution. The method developed here is generally applicable to revealing the structure–activity correlation of electrochemical reactions at grain boundaries.