(378f) Electrochemical Studies of Low Temperature Ionic Liquid-Cosolvent-Salt Electrolyte Systems

Ionic liquids (IL), consist of ions and remain as liquid at ambient temperatures, have shown potentials as electrolytes in a great variety of applications. Their characteristic traits (low phase transition temperature, low volatility, good stability, etc.) broaden the operational temperature range on both high and low ends, while incorporations with other solvents and salts appear to be a common strategy for optimizations and enhancements on both physicochemical and electrical properties. Understandings in electrochemical properties of the IL-cosolvent-salt systems, developed for molecular electronic transducer (MET) seismometer to conduct seismology studies under extreme conditions, are crucial for evaluations of the functionality and future improvements. In this work, we present new findings in electrochemical aspects relevant to performances of the MET seismometer, specifically on the ionic conductivity and electrochemical stability. The electrochemical impedance spectroscopy technique was employed to measure the conductivity evolution from room temperature to around -70 ËšC. The results revealed that the ionic conductivity resembled an Arrhenius behavior, and did not show significant breakdowns before reaching the glass transition temperature (Tg). Cyclic voltammetry was applied to study the electrochemical windows, with platinum as the working electrode. Within an appropriate potential window, iodide (I^-)/triiodide (I₃^-) redox species reacted and generated currents without additional undesired electrochemical reactions occurred. The current best developed IL-water-salt electrolyte system demonstrates a desirable conductivity ranging from room temperature to -70 ËšC, and a good electrochemical stability under an properly applied voltage. In addition to electrochemistry investigations, results from computational works provide insights of interactions on the molecular level and possible explanations for observed phenomena. Discoveries of the presented works may serve as a reference for MET seismometer applications, and other low temperature electrochemical devices operating based on the I^-/I₃^- redox pairs.