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

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 (CDL) was estimated.