Inherent Promotion of Ionic Conductivity via Coherent Vibrational Strong Coupling of Water

The vibrational strong coupling, where vibrational energy states of molecules and an optical cavity mode are hybridized, is an emerging method for the modification of ground-state thermochemical reactivity of molecules. Here, we report that vibrational strong coupling promotes ionic conductivity of aqueous electrolyte. A Fabry-Pérot cavity were fabricated for the spectroscopic analysis and electrochemical impedance measurements of electrolyte solution. We observed the splitting of vibrational state of water in optical cavity with the Rabi splitting energy of 760 cm−1 by matching cavity mode frequency to OH stretching mode frequency of water molecules. From the electrochemical impedance measurements, we discovered the modulation of relative dielectric constants and one-fold promotion of proton conductivity of the aqueous electrolyte. This study demonstrates that the use of vibrational strong coupling system for the promotion of ionic conductivity utilized for the electrochemical energy conversion system without light pumping.