Surface Charge Regulated Asymmetric Ion Transport in Nanoconfined Space.

The asymmetric ion transport in the nanoconfined space, similar to that of natural ion channels, has attracted broad interest in sensor, energy conversion, and other related fields. Among these systems, the surface charge plays an important role in regulating ion transport behaviors. Herein, this surface charge-regulated asymmetric ion transport behavior is systematically explored in the nanoconfined space and the influence on the performance of nanofluidic energy conversion system. The ion transport behaviors in the nanoconfined space are classified into pure diffusion, electrical double layer, and the polarization controlled state. The asymmetric solution environment or surface charge distribution induces asymmetric ion transport behavior which is largely controlled by the low concentration side. The ion-selectivity and the energy conversion performance can be effectively enhanced by improving the local apparent surface charge (more active sites and higher charge strength) or introducing a selective layer with dense surface charge on the low concentration side. These material design concepts for asymmetric ion transport are further supported by both simulation and experiment. The results provide a significant comprehension for ion behaviors in nanoconfined space and the development of high-performance energy storage and conversion systems.