Enhanced charge transport in nano-confined ionic liquids

Charge transport in ionic liquids contained in unidirectional nanoporous membranes (pore diameters: 7.510.4 nm) is investigated by combining broadband dielectric spectroscopy (BDS) and pulsed field gradient (PFG)-NMR. This enables one to determine the diffusion coefficient and the diffusion rate over more than 13 decades and to trace its temperature dependence. Under conditions of nanometric confinement, a change from a VogelFulcherTammann into an Arrhenius-like thermal activation is observed, resulting in an enhancement of diffusivities by more than two orders of magnitude. The effect becomes more pronounced with decreasing pore diameter. It is attributed to changes in molecular packing and hence in density leading to higher mobility and electrical conductivity. Diffusion coefficients of ionic liquids increase by over two orders of magnitude under nanometric confinement.