Observation of Electric-Field-Induced Liberation of Guest Molecules from Clathrate Hydrate

Clathrate hydrates can store a high density of guest molecules in cages. However, as a gas-storage material, the controllable release of guests therefrom is still challenging. Here we report on the utilization of an electric field as a control agent. Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is used to investigate the release of tetrahydrofuran (THF) from the clathrate in the electrochemical double layer (EDL). When voltage is applied, the ATR-SEIRA signal from encaged THF rapidly decreases, and the water characteristic O-H absorption peak exhibits an appreciable blue-shift. Our measurements indicate a transformation of the hydrate lattice to a less H-bonded configuration at the electrode surface. In combination with previous experimental results on the orientation of water molecules in the EDL, we propose that the strong electric field in the EDL aligns the water molecules of the clathrate and distorts the hydrate lattice structure enough to release the trapped guest molecules.