Potential-independent electron transfer rate at the liquid/liquid interface

Electron transfer (ET) from neutral zinc porphyrin (ZnPor) molecules in various organic solvents to aqueous redox species (e.g., Ru(CN)(6)(3-)) was probed by the scanning electrochemical microscope (SECM). Unlike previous studies in which organic redox species were charged, the ET rate was found to be essentially independent of the potential drop across the interfacial boundary. This difference is explained by diffuse double-layer effect predicted by known models of the liquid/liquid interface. The effect of solvent dynamics on the rate of ET at the liquid/liquid interface was observed for the first time. The high precision and sensitivity of the SECM allow one to detect complexity in an interfacial reaction that may not be obvious from other electrochemical measurements and select a suitable system for checking the ET theory.