Hysteresis of Potential-Dependent Changes in Ion Density and Structure of an Ionic Liquid on a Gold Electrode: In Situ Observation by Surface-Enhanced Infrared Absorption Spectroscopy

Potential-dependent structure and dynamics of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([BMIM][TFSA]) on an Au electrode have been investigated by using surface-enhanced infrared absorption spectroscopy (SEIRAS). In situ, real-time IR measurements during potential scans enable us to probe a hysteretic exchange and reorientation of both the cation and anion at the interface simultaneously owing to the high interface selectivity and sensitivity of SEIRAS. Our experimental results reveal that during potential scans, the ion density in overlayers changes first, and then the exchange of the ions in the first ionic layer occurs to compensate the changes in surface charge.