In Situ Electrochemical SFG/DFG Study of CN-- and Nitrile Adsorption at Au from 1-Butyl-1-methyl-pyrrolidinium Bis(trifluoromethylsulfonyl) Amide Ionic Liquid ([BMP][TFSA]) Containing 4-{2-[1-(2-Cyanoethyl)-1,2,3,4-tetrahydroquinolin-6-yl]diazenyl} Benzonitrile (CTDB) and K[Au(CN)$_2$]

TL;DR

This study uses in situ electrochemical SFG/DFG spectroscopy to investigate nitrile and CN-- adsorption on gold electrodes in an ionic liquid, revealing potential-dependent vibrational features and the influence of electrodeposition on adsorption behavior.

Contribution

It provides new insights into nitrile and CN-- adsorption mechanisms on gold in ionic liquids using in situ vibrational spectroscopy during electrochemical processes.

Findings

Potential-dependent SFG bands indicate nitrile and CN-- adsorption behavior.

Electrodeposition affects Stark tuning and adsorption properties.

CTDB inhibits cathodic reactions, influencing surface chemistry.

Abstract

In this paper we report an in situ electrochemical Sum-/Difference Frequency Generation (SFG/DFG) spectroscopy investigation of the adsorption of nitrile and CN -- from the ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP][TFSA]) containing 4-{2-[1-(2-cyanoethyl)-1,2,3,4-tetrahydroquinolin-6-yl]-diazenyl}benzonitrile (CTDB) at Au electrodes in the absence and in the presence of the Au-electrodeposition process from K[Au(CN)$_2$ ]. The adsorption of nitrile and its coadsorption with CN -- resulting either from the cathodic decomposition of the dye or from ligand release from the Au(I) cyanocomplex yield potential-dependent single or double SFG bands in the range 2,125-2,140 cm$^{-1}$, exhibiting Stark tuning values of ca. 3 and 1 cm$^{-1}$ V$^{-1}$ in the absence and presence of electrodeposition, respectively. The low Stark tuning found during electrodeposition correlates with the cathodic inhibiting effect of CTDB, giving rise to its levelling properties. The essential insensitivity of the other DFG parameters to the electrodeposition process is due to the growth of smooth Au.