A routine schematic in every general chemistry textbook shows individual electrons and metal ions undergoing reactions, diffusion, and dissolution at a pair of spatially-distinct electrodes — the cathode and anode — at a metal/solution interface. Yet, the correlation between the anode and cathode over both space and time has never been directly measured at the molecular scale. Current technologies are limited by focusing only on the electron transfer half of the reaction (voltammetry), are <i>ex situ</i> or near-field (electron or scanning probe microscopies), or detect macroscale material changes (industrial standards). Here, I will discuss single-molecule experimental and statistical methods that reveal the detailed physical relationship between anodic and cathodic reactions at liquid/metal interfaces. <i>In situ</i> charge transfer is observed using fluorescent dyes that “turn-on” upon either receiving an electron or metal ion. Super-resolution analysis of the dyes determines the locations of both the cathode and anode at ~10’s nm spatial and ~1’s ms temporal resolutions, revealing that charge is transferred across the interface of iron and iron alloy surfaces by ions in addition to electrons.

Molecular physical electrochemistry at interfaces: Visualizing charge transfer at the anode and cathode

ACS Spring 2022

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