Molecular insight into the dynamics at the lithium-containing ionic liquid/gold film electrode interface using electrochemical attenuated total reflection spectroscopies

Abstract

The spectral response at the interface between lithium-containing 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI) and a gold electrode was investigated using electrochemical attenuated total reflection spectroscopy (EC-ATR) in the far-ultraviolet and infrared regions. At a negatively charged Au electrode within the cathodic limit, an increase in the EMIM cation signal and a decrease in the TFSI anion signal were observed for neat EMIM-TFSI, indicating the normal replacement of the TFSI anions by the EMIM cations. In contrast, an apparent decrease in the EMIM cation signal and an increase in the TFSI anion signal were observed, suggesting the replacement of the EMIM cation with a Li⁺ cation coordinated with TFSI anions. The ATR spectral responses were reversible in the electrode potential cycles, likely due to diffusion perpendicular to the electrode or the reorientation of the interfacial ionic liquid components. The surface-stabilized Li⁺ ions coordinated by the TFSI anions at the negatively charged Au electrode may restrict the direct interaction of the EMIM cation with the electrode, thereby reducing the reduction rate of the EMIM cation, and extending the cathodic limit upon the addition of the Li salt.