Surface Electrochemistry of Au(111) in Acetonitrile Based Electrolytes: Formation of a Solvent Related Adsorbed Layer

Fundamental understanding of the electrochemistry at metal/nonaqueous solvent interfaces is of importance both for improving organic solvent based electrochemical devices and also for generalizing theories of interfacial electrochemistry that were developed based on aqueous solvents. Herein we report electrochemical characterization of the Au(111)/acetonitrile (ACN) interface in verifiably clean conditions, in a potential region normally considered nonreactive or ideally polarizable. We demonstrate the formation of a solvent related adsorbed layer on the Au(111) surface upon contact with the electrolyte, which further undergoes oxidative and reductive transformations in subsequent cyclic voltammetry. The presence of this layer is further confirmed by ex situ electrochemical characterization and X-ray photoelectron spectroscopy. We also show how the composition of the adsorbed layer depends on the electrolyte composition and the applied electrochemical program. Taken together, these results show that the adsorbed layer incorporates both (decomposed) acetonitrile and electrolyte ions and that the Au(111)/ACN interface cannot be considered ideally polarizable. Our findings represent a significant step toward a more precise understanding of the interfacial electrochemistry of the Au(111)/ACN interface and demonstrate the importance of interphase layers in the general understanding of nonaqueous surface electrochemistry.