Boosting the mobility of ions in nanoporous confinement by applying a gate voltage.

The mobility of ions under confinement in nanoporous host materials is central to many electrochemical energy transformation and storage devices. By using ionic liquids (ILs) as electrolytes and metal-organic frameworks (MOFs) as well-defined, regular nanoporous hosts, the dynamic ion properties were explored in detail. Here, we demonstrate for the first time that applying a gate-voltage (perpendicular to the charge transfer direction) allows the ion mobilities to be considerably enhanced. The experiments, which are based on MOF films, show a conductivity increase of up to 35%. In addition, molecular dynamics simulations provide deeper insights, showing that the gate-voltage-field causes layers of increased and decreased ion concentrations, parallel to the charge transfer direction. In these layers, the ion mobilities is up to 2.5 times higher than that in the bulk phase or without an additional gate-voltage field. Thus, these layers of highly mobile ions could be referred to as gate-voltage-induced "ion highways", causing the experimentally observed higher conductance. Moreover, a general correlation between the ion mobilities and the local ion concentration was found. The study provides deeper insights into ion dynamics in nanoporous confinement and provides a method for enhanced ion mobilities.