Void-assisted ion-paired proton transfer at water-ionic liquid interfaces

Abstract

At the water-trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ([P14,6,6,6][FAP]) ionic liquid interface, the unusual electrochemical transfer behavior of protons (H+) and deuterium ions (D+) was identified. Alkali metal cations (such as Li+, Na+, K+) did not undergo this transfer. H+/D+ transfers were assisted by the hydrophobic counter anion of the ionic liquid, [FAP]-, resulting in the formation of a mixed capacitive layer from the filling of the latent voids within the anisotropic ionic liquid structure. This phenomenon could impact areas such as proton-coupled electron transfers, fuel cells, and hydrogen storage where ionic liquids are used as aprotic solvents. Protons squeezing through the interface: At the water/ionic liquid interface, size-dependent transfer of protons into voids of the ionic liquid phase occurs with electrochemical control. These results can have implications in a variety of proton transfer reactions, such as in fuel cells and hydrogen storage.