(462f) Development of an Ionic Liquid Based Low-Temperature Electrolyte System for Sensing Applications of Planetary Exploration

It is of great importance to understand the interior structure and the composition of other planets via seismological studies for a foreign planet. The molecular electronic transducer (MET) technology has been utilized in designing planetary seismometers that use liquid electrolyte to enable the higher shock tolerance and independence of installation angle during deployment, comparing to conventional spring-mass based systems. However, it is challenging to adapt MET sensors using any aqueous-based electrolyte to the extreme low-temperature environments on planets such as Europa.

Ionic liquids have a wide liquid temperature range and are highly ionic conductive, non-volatile, and electrochemically stable, making them a class of materials as the excellent candidate for electrolytes for a variety of applications. Despite the advantages, the drawbacks of using ionic liquids as electrolyte materials for space applications include their relatively high viscosity and undesired thermal events, which can both contribute to depressing the charge transport in the electrolyte, especially when operating at low temperatures. Herein, we report a liquid electrolyte system based on a mixture of the ionic liquid 1-butyl-3-methylimidazolium iodide ([BMIM][I]) and water with incorporation of an alkylammonium-based ionic liquid for the planetary application of MET sensors at extremely low temperatures. The properties of thermal, mass transport, and conductivity of developed electrolyte solutions were examined at varying temperatures down to –75 °C. The effect of incorporating alkylammonium-based ionic liquid into the [BMIM][I]/water mixture at the optimized concentration can effectively prevent the formation of crystallization within the solution, which is critical in employing ionic liquids as electrolytes for any low-temperature applications, and also further tune the properties of the electrolyte by lowering the glass transition temperature, reducing viscosity, and enhancing the conductivity. The electrochemical stability of the selected candidate formulations was studied via cyclic voltammetry, showing that the incorporation of the alkylammonium-based ionic liquid did not appear to introduce undesired redox reactions and the ILs-water-salt system didn’t suffer from additional electrochemical reactions other than iodide/triiodide redox within a proper potential window. The results of this presented work will not only extend the MET sensing technology to the field of space exploration but also allow the potential applications of other electrochemical devices with iodide/triiodide redox pairs at low temperatures.