Unlimiting Ionic Conduction: Manipulating Hydration Dynamics through Vibrational Strong Coupling of Water

The energy states of molecules and the vacuum electromagnetic field can hybridize to form a strong coupling state. In particular, it has been demonstrated that vibrational strong coupling can be used to modify the chemical dynamics of molecules. Here, we propose that ion dynamics can be altered through modifications of the dynamic hydration structure in a cavity vacuum field. We conducted investigations on various electrolyte species to explore their impact on ionic conductivity. Infrared spectroscopy of aqueous electrolyte solutions within the cavity confirmed the occurrence of vibrational ultra-strong coupling behavior of water molecules, even in the presence of electrolytes. Interestingly, we observed significant enhancements in ionic conductivity, several times greater for alkali cations, particularly those classified as structure-breaking cations. These enhancements are both feasible and cannot be explained within the current theoretical framework for liquid electrolytes. Our analysis confirmed that the vibrational strong coupling leads to the modification of local dielectric friction experienced by hydrated ions. Additionally, we propose the enthalpic and entropic modifications of ionic conductivity through systematic investigations of electrolytes and their hydration properties. This study unveiled the potential role of polaritons in opening up possibilities for exploring uncharted spaces in the design of materials for enhanced ionic conduction. By harnessing the unique properties of strong coupling and its influence on hydration dynamics, we can pave the way for the development of novel electrolytes and advancements in the field of ionic conduction.