Rate and mechanism of thiolate deligation in Au ₂₅ nanoclusters <i>via in operando</i> electrochemical impedance spectroscopy

Nanomaterial electrocatalysis is a critical field for advancing sustainable energy technologies, yet determining the active catalytic species remains a significant challenge as the active species is often a result of dynamic structural evolution of the catalyst during the reaction. In this work, we investigate reductive deligation, a well-known activation process of ligated nanomaterials, on [Au₂₅(PET)₁₈]^- (PET = 2-phenylethanethiol) nanoclusters (Au₂₅) under varying electrochemical conditions. We introduce a novel application of electrochemical impedance spectroscopy (EIS) to characterize the Au₂₅ <i>in situ</i> throughout the reductive deligation process, which we term <i>in operando</i> EIS. This approach enables real-time monitoring of ligand removal by extracting key parameters such as the charge-transfer resistance. By systematically varying applied potential and pH, we gain kinetic and mechanistic insight into Au₂₅ deligation and provide experimental evidence that protons play an important role in this transformation. Ultimately, this study establishes <i>in operando</i> EIS as a powerful electrochemical characterization tool for monitoring <i>in situ</i> catalyst evolution and deepens our understanding of Au₂₅ deligation behavior.