Preferential Electroreduction at the Oil|Water|Conductor Interface

Chemistry in confined volumes, such as aqueous droplets, is different from bulk, continuous water. However, few techniques are available to probe interfacial reactivity in complex, multiphase environments. Here, we demonstrate preferential electroreduction at the oil|water|conductor (three-phase) interface. Electrodeposition of cobalt and nickel results in ring-like structures that can be characterized with tens of nanometer precision in scanning electron microscopy and energy dispersive x-ray spectroscopy. To demonstrate the generalizability of these observations, we demonstrate that electroreduction of resazurin to fluorescent resorufin occurs preferentially at the three-phase boundary and does not strongly depend on droplet geometry. We suggest that our observations can be explained by adsorption to the liquid|liquid interface and the interfacial electric field. These results, grounded in three-phase boundary reactivity, are highly important across all fields of chemistry and biology because they highlight how the interface can change chemistry in unexpected ways.