An SFG/DFG investigation of CN− adsorption at an Au electrode in 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) amide ionic liquid

Abstract In this paper we report an SFG/DFG investigation of the adsorption of CN − – used as a probe molecule to study the electrochemical double-layer structure – at a polycrystalline Au electrode in 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP][TFSA]) room-temperature ionic liquid (RTIL). The adsorption of CN − yielded single SFG and DFG bands in the range from ca. 2125 to 2135 cm −1 , exhibiting a Stark tuning of ca. 3 cm −1  V −1 . Vibrational resonances – corresponding to modes of the RTIL coadsorbed with CN − , were found in the range from ca. 1200 to 1500 cm −1 . The study of the double-layer structure was complemented by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements, from which the differential double-layer capacity ( C DL ) was estimated.