Local Electric Fields and Chemical Environment at the Electrode-Ionic Liquid Interface Measured via Vibrational Sum Frequency Generation.

The conductor-electrocyte interface is the main stage for all electrochemical catalysis. At this junction, interfacial electric fields are intimately related to molecular structure and, therefore, influence electrochemistry. To understand this relation, it is necessary to directly probe the local electric field and chemical environment of an interface. We use a well-known vibrational chromophore both as a Stark shift reporter of electric fields and as a probe of the chemical environment present at the electrode-ionic liquid interface. In both cases, we monitor vibrational frequency changes of the chromophore using vibrational sum frequency generation (VSFG). In the first case, we show that electric field strengths of approximately 19 MV/cm are present at the interface. Additionally, we will examine how the ionic liquid anion size affects these fields. In the second case, we will examine how the the addition of water, a common proton source used in ionic liquid electrochemistry, changes the ionic liquid structure at the interface.