Site-Specific Stochastic\nRates and Energetics of Ag\nNucleation on Highly Ordered Pyrolytic Graphite

Nucleation is a fundamentally important step in electrochemical\nphase transition reactions, e.g., in electrodeposition, which is pertinent\nfor emerging battery technology, nanoparticle synthesis, and many\nindustrial processes. Surface defects have been suggested to enhance\nnucleation rates. However, directly quantifying the nucleation rates\nat specific surface sites is challenging due to the ensemble averaging\neffect in bulk measurements. Herein, we report the measurement of\nrates and energetics of electronucleation across the model surface\nof highly oriented pyrolytic graphite (HOPG). Specifically, scanning\nelectrochemical cell microscopy (SECCM) is used to confine the nucleation\nspatially in the nanoscale cell, allowing one nucleation event to\nbe measured at one time. The scanning capability further allows the\nmapping of Ag nucleation at the step edge vs basal plane. A stochastic\nmodel is developed to extract the nucleation rate and energetics from\nvoltammetric experiments. We observed a ∼57 mV difference in\nthe median nucleation overpotential between the step edge and basal\nplane, corresponding to a ∼12 kJ mol<sup>–1</sup> difference\nin the nucleation energy barrier. The voltammetric method to measure\nthe nucleation rate explored here can be extended to understand the\nheterogeneity of nucleation rates in other electrochemical nucleation\nsystems, e.g., metal anode batteries.