In situ ATR-SEIRAS investigations on the effects of Li+ and dissolved O2 on electrochemical interfacial reorganisation in an ionic liquid

Abstract

Interfacial reorganisation at a gold electrode within an ionic liquid (1-methyl-1-propylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide, ([Pyrr13][TFSI])) electrolyte was investigated via in situ electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The in situ cell incorporated a micromachined Si wafer internal reflection element, that enabled the spectral recording down to 500 cm-1. Cation-anion restructuring of the double layer in the aprotic ionic liquid, [Pyrr13][TFSI], was explored under varying potential windows within the extended wavenumber range of 4000-500 cm-1. Double layer restructuring was found to be significantly impeded by inclusion of low concentrations of Li-salt (0.001 M Li[TFSI]). The presence of Li+ led to the formation of [Li[TFSI]x](x-1) complexes and aggregates which disrupt the periodicity of the double layer of the neat ionic liquid. The inclusion of dissolved O2 into [Pyrr13][TFSI] led to irreversible promotion of double layer rearrangement with the redox active solute with coordinating properties with cation (O2- ---[Pyrr13]+).